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The Julian calendar, proposed by
Julius Caesar Gaius Julius Caesar (; 12 July 100 BC – 15 March 44 BC) was a Roman Roman or Romans usually refers to: *Rome, the capital city of Italy *Ancient Rome, Roman civilization from 8th century BC to 5th century AD *Roman people, the people of anc ...

Julius Caesar
in , was a reform of the
Roman calendar The Roman calendar was the calendar used by the Roman kingdom and Roman Republic, republic. The term often includes the Julian calendar established by the reforms of the Roman dictator, dictator Julius Caesar and Roman emperor, emperor August ...
. It took effect on , by
edict An edict is a decree or announcement of a law, often associated with monarchy, monarchism, but it can be under any official authority. Synonyms include "dictum" and "pronouncement". ''Edict'' derives from the Latin wikt:edictum#Latin, edictum. N ...
. It was designed with the aid of Greek mathematicians and
astronomers An astronomer is a scientist in the field of astronomy Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a natural science that studies astronomical object, celestial objects ...
such as
Sosigenes of Alexandria Sosigenes of Alexandria ( grc-gre, Σωσιγένης ὁ Ἀλεξανδρεύς) was a Greek astronomer from Ptolemaic Egypt who, according to Roman historian Pliny the Elder, was consulted by Julius Caesar for the definition of the Julian calend ...
. The calendar became the predominant calendar in the
Roman Empire The Roman Empire ( la, Imperium Rōmānum ; grc-gre, Βασιλεία τῶν Ῥωμαίων, Basileía tôn Rhōmaíōn) was the post-Republican Republican can refer to: Political ideology * An advocate of a republic, a type of governme ...

Roman Empire
and subsequently most of the
Western world The Western world, also known as the West, refers to various s, s and , depending on the context, most often consisting of the majority of , , and .
Western world
for more than 1,600 years until 1582, when
Pope Gregory XIII Pope Gregory XIII ( la, Gregorius XIII; 7 January 1502 – 10 April 1585), born Ugo Boncompagni, was head of the Catholic Church The Catholic Church, also known as the Roman Catholic Church, is the , with 1.3 billion Catholics . ...

Pope Gregory XIII
promulgated a minor modification to reduce the average length of the year from 365.25 days to 365.2425 days and thus corrected the Julian calendar's drift against the
solar year A tropical year (also known as a solar year or tropical period) is the time Time is the continued of and that occurs in an apparently succession from the , through the , into the . It is a component quantity of various s used to event ...
. Worldwide adoption of this revised calendar, which became known as the
Gregorian calendar The Gregorian calendar is the used in most of the world. It was introduced in October 1582 by as a modification of the , reducing the average year from 365.25 days to 365.2425 days, and adjusting for the drift in the that the inaccuracy ha ...
, took place over the subsequent centuries, first in
Catholic The Catholic Church, also known as the Roman Catholic Church, is the largest Christian church, with 1.3 billion baptised Baptism (from the Greek language, Greek noun βάπτισμα ''báptisma'') is a Christians, Christian r ...

Catholic
countries and subsequently in
Protestant Protestantism is a form of that originated with the 16th-century , a movement against what its followers perceived to be in the . Protestants originating in the Reformation reject the Roman Catholic doctrine of , but disagree among themselves ...
countries of the Western Christian world. The Julian calendar is still used in parts of the
Eastern Orthodox Church The Eastern Orthodox Church, also called the Orthodox Church, is the second-largest Christian church, with approximately 220 million baptised members. It operates as a communion Communion may refer to: Religion * The Eucharist (also cal ...
and in parts of
Oriental Orthodoxy The Oriental Orthodox Churches are a group of Eastern Christian Eastern Christianity comprises Christian Christians () are people who follow or adhere to Christianity, a monotheistic Abrahamic religion based on the life and teachings ...
as well as by the
Berbers Berbers or ''Imazighen'' ( ber, translit=Imaziɣen, ⵉⵎⴰⵣⵉⵖⵏ, ⵎⵣⵗⵏ; singular: , ) are an ethnic group mostly concentrated in North Africa, specifically Morocco, Algeria, Tunisia, Libya, the Canary Islands, and to a lesser ...

Berbers
. The Julian calendar has two types of years: a normal year of 365 days and a leap year of 366 days. They follow a simple cycle of three normal years and one leap year, giving an average year that is 365.25 days long. That is more than the actual
solar year A tropical year (also known as a solar year or tropical period) is the time Time is the continued of and that occurs in an apparently succession from the , through the , into the . It is a component quantity of various s used to event ...
value of 365.24219 days (the current value, which varies) which means the Julian calendar gains a day every 128 years. For any given event during the years from 1901 to 2099 inclusive, its date according to the Julian calendar is 13 days behind its corresponding Gregorian date.


Table of months


History


Motivation

The ordinary year in the previous Roman calendar consisted of 12 months, for a total of 355 days. In addition, a 27- or 28-day
intercalary month Intercalation or embolism in timekeeping is the insertion of a leap day, week, or month into some calendar years to make the calendar follow the seasons or moon phases. Lunisolar calendar A lunisolar calendar is a calendar in many culture Cul ...
, the Mensis Intercalaris, was sometimes inserted between February and March. This intercalary month was formed by inserting 22 or 23 days after the first 23 days of February; the last five days of February, which counted down toward the start of March, became the last five days of Intercalaris. The net effect was to add 22 or 23 days to the year, forming an intercalary year of 377 or 378 days. Some say the ''mensis intercalaris'' always had 27 days and began on either the first or the second day after the Terminalia (23 February). According to the later writers
Censorinus Censorinus was a Roman grammarian and miscellaneous writer from the 3rd century AD. He was the author of a lost work ''De Accentibus'' and of an extant treatise ''De Die Natali'', written in 238, and dedicated to his patron Quintus Caerellius ...

Censorinus
and
Macrobius Macrobius Ambrosius Theodosius, usually referred to as Macrobius (fl. AD 400), was a Roman provincial who lived during the early fifth century, during Late Antiquity, the period of time corresponding to the late Roman Empire The history of the ...

Macrobius
, the ideal intercalary cycle consisted of ordinary years of 355 days alternating with intercalary years, alternately 377 and 378 days long. In this system, the average Roman year would have had days over four years, giving it an average drift of one day per year relative to any
solstice A solstice is an event that occurs when the Sun appears to reach its most northerly or southerly excursion relative to the celestial equator on the celestial sphere In astronomy and navigation, the celestial sphere is an abstraction, abstr ...

solstice
or equinox. Macrobius describes a further refinement whereby, in one 8-year period within a 24-year cycle, there were only three intercalary years, each of 377 days (thus 11 intercalary years out of 24). This refinement averages the length of the year to 365.25 days over 24 years. In practice, intercalations did not occur systematically according to any of these ideal systems, but were determined by the
pontifices A pontiff (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman R ...
. So far as can be determined from the historical evidence, they were much less regular than these ideal schemes suggest. They usually occurred every second or third year, but were sometimes omitted for much longer, and occasionally occurred in two consecutive years. If managed correctly this system could have allowed the Roman year to stay roughly aligned to a tropical year. However, since the pontifices were often politicians, and because a Roman magistrate's term of
office An office is a space where an Organization, organization's employees perform Business administration, administrative Work (human activity), work in order to support and realize objects and Goals, plans, action theory, goals of the organizatio ...

office
corresponded with a calendar year, this power was prone to abuse: a pontifex could lengthen a year in which he or one of his political allies was in office, or refuse to lengthen one in which his opponents were in power. If too many intercalations were omitted, as happened after the
Second Punic War The Second Punic War, which lasted from 218 to 201BC, was the second of three wars fought between Carthage Carthage was the capital city of the ancient , on the eastern side of the in what is now . Carthage was the most important trading ...

Second Punic War
and during the
Civil Wars A civil war, also known as an intrastate war in polemology, is a war War is an intense armed conflict between states State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine publish ...
, the calendar would drift out of alignment with the tropical year. Moreover, because intercalations were often determined quite late, the average Roman citizen often did not know the date, particularly if he were some distance from the city. For these reasons, the last years of the pre-Julian calendar were later known as "years of confusion". The problems became particularly acute during the years of Julius Caesar's pontificate before the reform, 63–46 BC, when there were only five intercalary months (instead of eight), none of which were during the five Roman years before 46 BC. Caesar's reform was intended to solve this problem permanently, by creating a calendar that remained aligned to the sun without any human intervention. This proved useful very soon after the new calendar came into effect.
Varro Marcus Terentius Varro (; 116–27 BC) was a Roman polymath A polymath ( el, πολυμαθής, , "having learned much"; la, homo universalis, "universal human") is an individual whose knowledge spans a substantial number of subjects, known ...
used it in 37 BC to fix calendar dates for the start of the four seasons, which would have been impossible only 8 years earlier.Varro
''On Agriculture'' I.1.28.
/ref> A century later, when
Pliny Pliny may refer to: People from antiquity * Pliny the Elder (AD 23–79), ancient Roman nobleman, scientist, historian, and author of ''Naturalis Historia'' (''Pliny's Natural History'') * Pliny the Younger (died 113), ancient Roman statesman, ...

Pliny
dated the
winter solstice The winter solstice, also called the hibernal solstice, occurs when either of Earth's geographical pole, poles reaches its maximum axial tilt, tilt away from the Sun. This happens twice yearly, once in each hemisphere (Northern Hemisphere, Nort ...

winter solstice
to 25 December because the sun entered the 8th degree of Capricorn on that date, this stability had become an ordinary fact of life.


Context of the reform

Although the approximation of days for the tropical year had been known for a long time, ancient
solar calendar A solar calendar is a calendar A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A calendar date, date is the designation of a single, specific day with ...
s had used less precise periods, resulting in gradual misalignment of the calendar with the seasons. The
octaeterisIn astronomy Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a natural science that studies astronomical object, celestial objects and celestial event, phenomena. It uses mathem ...
, a cycle of eight lunar years popularised by
Cleostratus:''This article concerns the Greek astronomer. For the article on the lunar crater named for him, see Cleostratus (crater).'' Cleostratus ( el, Κλεόστρατος; b. c. 520 BC; d. possibly 432 BC) was an astronomer of ancient Greece. He was a ...
(and also commonly attributed to Eudoxus) which was used in some early Greek calendars, notably in
Athens , image_skyline = File:Athens Montage L.png, center, 275px, alt=Athens montage. Clicking on an image in the picture causes the browser to load the appropriate article. rect 15 15 985 460 Acropolis of Athens rect 15 475 48 ...
, is 1.53 days longer than eight mean Julian years. The length of nineteen years in the was 6,940 days, six hours longer than the mean Julian year. The mean Julian year was the basis of the 76-year cycle devised by Callippus (a student under Eudoxus) to improve the Metonic cycle. In Persia (Iran) after the reform in the
Persian calendar The Iranian calendars or Iranian chronology ( fa, گاه‌شماری ایرانی, ''Gāh-Šomāri-ye Irāni'') are a succession of calendars invented or used for over two millennia in Iran Iran ( fa, ایران ), also called Persia ...
by introduction of the Persian Zoroastrian (i. e. Young Avestan) calendar in 503 BC and afterwards, the first day of the year (1 Farvardin=
Nowruz Nowruz ( fa, نوروز, ; ) is the Iranian New Year, also known as the Persian New Year, which begins on the spring equinox, marking the first day of Farvardin Farvardin ( fa, فروردین, ) is the Iranian Persian name for the first mont ...

Nowruz
) slipped against the vernal equinox at the rate of approximately one day every four years. Likewise in the
Egyptian calendar The ancient Egyptian calendar – a civil calendar – was a solar calendar A solar calendar is a calendar A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and ...
, a fixed year of 365 days was in use, drifting by one day against the sun in four years. An unsuccessful attempt to add an extra day every fourth year was made in 238 BC (
Decree of CanopusThe Decree of Canopus is a trilingual inscription in three scripts, which dates from the Ptolemaic period of ancient Egypt Ancient Egypt was a civilization of Ancient history, ancient North Africa, concentrated along the lower reaches of th ...
). Caesar probably experienced this "wandering" or "vague" calendar in that country. He landed in the Nile delta in October 48 BC and soon became embroiled in the Ptolemaic dynastic war, especially after
Cleopatra Cleopatra VII Philopator ( grc-gre, Κλεοπάτρα Φιλοπάτωρ}; 69 BC10 August 30 BC) was queen of the Ptolemaic Kingdom of Ancient Egypt, Egypt from 51 to 30 BC, and its last active ruler.She was also a diplomat, Ancient ...
managed to be "introduced" to him in
Alexandria Alexandria ( or ; ar, الإسكندرية ; arz, اسكندرية ; Coptic language, Coptic: Rakodī; el, Αλεξάνδρεια ''Alexandria'') is the List of cities and towns in Egypt, third-largest city in Egypt after Cairo and Giza, ...

Alexandria
. Caesar imposed a peace, and a banquet was held to celebrate the event.Lucan, ''
Pharsalia ''De Bello Civili'' (; ''On the Civil War''), more commonly referred to as the ''Pharsalia'', is a Roman literature, Roman Epic poetry, epic poem written by the poet Lucan, detailing the Caesar's civil war, civil war between Julius Caesar and th ...
:'
''Book 10''.
/ref>
Lucan Marcus Annaeus Lucanus (3 November 39 AD – 30 April 65 AD), better known in English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon E ...

Lucan
depicted Caesar talking to a wise man called Acoreus during the feast, stating his intention to create a calendar more perfect than that of Eudoxus (Eudoxus was popularly credited with having determined the length of the year to be days). But the war soon resumed and Caesar was attacked by the Egyptian army for several months until he achieved victory. He then enjoyed a long cruise on the Nile with Cleopatra before leaving the country in June 47 BC. Caesar returned to Rome in 46 BC and, according to
Plutarch Plutarch (; grc-gre, Πλούταρχος, ''Ploútarchos''; ; AD 46 – after AD 119) was a Greek Middle Platonist Middle Platonism is the modern name given to a stage in the development of Platonic philosophy, lasting from about 90 BC&nbs ...

Plutarch
, called in the best philosophers and mathematicians of his time to solve the problem of the calendar. Pliny says that Caesar was aided in his reform by the astronomer
Sosigenes of Alexandria Sosigenes of Alexandria ( grc-gre, Σωσιγένης ὁ Ἀλεξανδρεύς) was a Greek astronomer from Ptolemaic Egypt who, according to Roman historian Pliny the Elder, was consulted by Julius Caesar for the definition of the Julian calend ...
who is generally considered the principal designer of the reform. Sosigenes may also have been the author of the astronomical almanac published by Caesar to facilitate the reform. Eventually, it was decided to establish a calendar that would be a combination between the old Roman months, the fixed length of the Egyptian calendar, and the days of Greek astronomy. According to Macrobius, Caesar was assisted in this by a certain Marcus Flavius.


Adoption of the Julian calendar

Caesar's reform only applied to the
Roman calendar The Roman calendar was the calendar used by the Roman kingdom and Roman Republic, republic. The term often includes the Julian calendar established by the reforms of the Roman dictator, dictator Julius Caesar and Roman emperor, emperor August ...
. However, in the following decades many of the local civic and provincial calendars of the empire and neighbouring client kingdoms were aligned to the Julian calendar by transforming them into calendars with years of 365 days with an extra day intercalated every four years. The reformed calendars typically retained many features of the unreformed calendars. In many cases, the New Year was not on 1 January, the leap day was not on the traditional bissextile day, the old month names were retained, the lengths of the reformed months did not match the lengths of Julian months, and, even if they did, their first days did not match the first day of the corresponding Julian month. Nevertheless, since the reformed calendars had fixed relationships to each other and to the Julian calendar, the process of converting dates between them became quite straightforward, through the use of conversion tables known as ''hemerologia''. Several of the reformed calendars are only known through surviving hemerologia. The three most important of these calendars are the Alexandrian calendar and the
Ancient Macedonian calendar The Ancient Macedonian calendar is a lunisolar calendar A lunisolar calendar is a calendar in many culture Culture () is an umbrella term which encompasses the social behavior and Norm (social), norms found in human Society, societies, as well ...
─which had two forms: the Syro-Macedonian and the 'Asian' calendars. Other reformed calendars are known from
Cappadocia Cappadocia (; also ''Capadocia''; grc, label=Ancient Ancient history is the aggregate of past events
,
Cyprus Cyprus ; tr, Kıbrıs (), officially called the Republic of Cyprus,, , lit: Republic of Cyprus is an island country An island country or an island nation is a country A country is a distinct territory, territorial body or poli ...

Cyprus
and the cities of (Roman) Syria and Palestine. Most reformed calendars were adopted under Augustus, though the calendar of
Nabatea The Nabataean Kingdom ( ar, المملكة النبطية, al-Mamlakah an-Nabaṭiyyah), also named Nabatea (), was a political state of the Arab The Arabs (singular Arab ; singular ar, عَرَبِيٌّ, ISO 233: , Arabic pronunciation: , p ...
was reformed after the kingdom became the Roman province of Arabia in AD106. There is no evidence that local calendars were aligned to the Julian calendar in the western empire. Unreformed calendars continued to be used in
Gaul Gaul ( la, Gallia) was a region of Western Europe Western Europe is the western region of Europe Europe is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rat ...

Gaul
(the
Coligny calendar The Coligny calendar is a Gaulish Gaulish was an ancient Celtic language that was spoken in parts of Continental Europe Mainland or continental Europe is the contiguous continent of Europe, excluding its surrounding islands. It can a ...
), Greece, Macedon, the Balkans and parts of Palestine, most notably in Judea. The Alexandrian calendar adapted the Egyptian calendar by adding a 6th
epagomenal The intercalary month or epagomenal days. of the ancient Egyptian calendar, Egyptian, Coptic calendar, Coptic, and Ethiopian calendars are a period of five days in common years and six days in leap years in addition to those calendars' 12 standard ...
day as the last day of the year in every fourth year, falling on 29 August preceding a Julian bissextile day. It was otherwise identical to the Egyptian calendar. The first leap day was in 22 BC, and they occurred every four years from the beginning, even though Roman leap days occurred every three years at this time (see Leap year error). This calendar influenced the structure of several other reformed calendars, such as those of the cities of Gaza and Ascalon in Palestine, Salamis in Cyprus, and the province of Arabia. It was adopted by the
Coptic Orthodox Church The Coptic Orthodox Church ( cop, Ϯⲉⲕ̀ⲕⲗⲏⲥⲓⲁ ⲛ̀ⲣⲉⲙⲛ̀ⲭⲏⲙⲓ ⲛ̀ⲟⲣⲑⲟⲇⲟⲝⲟⲥ, translit=Ti.eklyseya en.remenkimi en.orthodoxos, lit=the Egyptian Orthodox Church; ar, الكنيسة القبطي ...

Coptic Orthodox Church
and remains in use both as the liturgical calendar of the Coptic church and as the civil calendar of
Ethiopia Ethiopia, officially the Federal Democratic Republic of Ethiopia, is a landlocked country A landlocked country is a country A country is a distinct territory, territorial body or political entity. It is often referred to as the ...

Ethiopia
. The Asian calendar was an adaptation of the
Ancient Macedonian calendar The Ancient Macedonian calendar is a lunisolar calendar A lunisolar calendar is a calendar in many culture Culture () is an umbrella term which encompasses the social behavior and Norm (social), norms found in human Society, societies, as well ...
used in the Roman province of Asia and, with minor variations, in nearby cities and provinces. It is known in detail through the survival of decrees promulgating it issued in 8BC by the proconsul
Paullus Fabius Maximus Paullus Fabius Maximus (died AD 14) was a Roman senator, active toward the end of the first century BC. He was consul Consul (abbrev. ''cos.''; Latin plural ''consules'') was the title of one of the two chief Roman magistrate, magistrates of the ...
. It renamed the first month Dios as , and arranged the months such that each month started on the ninth day before the kalends of the corresponding Roman month; thus the year began on 23 September, Augustus's birthday. Since Greek months typically had 29 or 30 days, the extra day of 31-day months was named —the emperor's day—and was the first day of these months. The leap day was a second Sebaste day in the month of Xandikos, i.e., 24 February. This calendar remained in use at least until the middle of the fifth century AD. The Syro-Macedonian calendar was an adaptation of the Macedonian calendar used in
Antioch Antioch on the Orontes (; grc, Ἀντιόχεια ἡ ἐπὶ Ὀρόντου, ''Antiókheia hē epì Oróntou''; also Syrian Antioch) grc-koi, Ἀντιόχεια ἡ ἐπὶ Ὀρόντου; or Ἀντιόχεια ἡ ἐπὶ Δάφνῃ ...
and other parts of
Roman Syria Roman Syria was an early Roman province The Roman provinces (Latin: ''provincia'', pl. ''provinciae'') were the administrative regions of Ancient Rome outside Roman Italy that were controlled by the Romans under the Roman Republic and late ...
. The months were exactly aligned to the Julian calendar, but they retained their Macedonian names and the year began in Dios (November) until the fifth century, when the start of the year was moved to Gorpiaios (September). These reformed calendars generally remained in use until the fifth or sixth century. Around that time most of them were replaced as civil calendars by the Julian calendar, but with a year starting in September to reflect the year of the
indiction An indiction ( la, indictio, impost) was a periodic reassessment of taxation in the Roman Empire which took place every fifteen years. In Late Antiquity, this 15-year cycle began to be used to date documents and it continued to be used for this pu ...
cycle. The Julian calendar spread beyond the borders of the Roman Empire through its use as the Christian liturgical calendar. When a people or a country converted to Christianity, they generally also adopted the Christian calendar of the church responsible for conversion. Thus, Christian Nubia and Ethiopia adopted the Alexandrian calendar, while Christian Europe adopted the Julian calendar, in either the Catholic or Orthodox variant. Starting in the 16th century, European settlements in the Americas and elsewhere likewise inherited the Julian calendar of the mother country, until they adopted the Gregorian reform. The last country to adopt the Julian calendar was the Ottoman Empire, which used it for financial purposes for some time under the name
Rumi calendar The ''Rumi'' calendar ( tr, Rumi takvim, lit. "Roman calendar"), a specific calendar based on the Julian calendar was officially used by the Ottoman Empire after Tanzimat (1839) and by its successor, the Republic of Turkey until 1926. It was adopt ...
and dropped the "escape years" which tied it to Muslim chronology in 1840.


Julian reform


Realignment of the year

The first step of the reform was to realign the start of the calendar year (1 January) to the tropical year by making 445 days long, compensating for the intercalations which had been missed during Caesar's pontificate. This year had already been extended from 355 to 378 days by the insertion of a regular
intercalary month Intercalation or embolism in timekeeping is the insertion of a leap day, week, or month into some calendar years to make the calendar follow the seasons or moon phases. Lunisolar calendar A lunisolar calendar is a calendar in many culture Cul ...
in February. When Caesar decreed the reform, probably shortly after his return from the in late Quintilis (July), he added 67 more days by inserting two extraordinary intercalary months between November and December.It is not known why he decided that 67 was the correct number of days to add, nor whether he intended to align the calendar to a specific astronomical event such as the winter solstice. Ideler suggested (''Handbuch der mathematischen und technischen Chronologie'' II 123–125) that he intended to align the winter solstice to a supposedly traditional date of 25 December. The number may compensate for three omitted intercalary months (67 = 22+23+22). It also made the distance from 1 March 46 BC, the original New Years Day in the Roman calendar, to 1 January 45 BC 365 days. These months are called ''Intercalaris Prior'' and ''Intercalaris Posterior'' in letters of
Cicero Marcus Tullius Cicero ( ; ; 3 January 106 BC – 7 December 43 BC) was a Ancient Rome, Roman statesman, lawyer, scholar, philosopher and Academic skepticism, Academic Skeptic, who tried to uphold optimate principles during crisis of ...

Cicero
written at the time; there is no basis for the statement sometimes seen that they were called " Undecimber" and " Duodecimber", terms that arose in the 18th century over a millennium after the Roman Empire's collapse.E.g., "... we have a sidelight on what was involved in "the year of confusion" as it was called. According to Dion Cassius, the historian, there was a governor in Gaul who insisted that, in the lengthened year, two months' extra taxes should be paid. The extra months were called Undecimber and Duodecimber." (P. W. Wilson
''The romance of the calendar''
(New York, 1937), 112). The eponymous dating of the cited passage

shows that it actually refers to an event of 15 BC, not 46 BC.
Their individual lengths are unknown, as is the position of the Nones and Ides within them. Because 46 BC was the last of a series of irregular years, this extra-long year was, and is, referred to as the "last year of confusion". The new calendar began operation after the realignment had been completed, in 45 BC.


Months

The Julian months were formed by adding ten days to a regular pre-Julian Roman year of 355 days, creating a regular Julian year of 365 days. Two extra days were added to January, Sextilis (August) and December, and one extra day was added to April, June, September, and November. February was not changed in ordinary years, and so continued to be the traditional 28 days. Thus, the ordinary (i.e., non-leap year) lengths of all of the months were set by the Julian calendar to the same values they still hold today. (See Sacrobosco's incorrect theory on month lengths (below) for stories purporting otherwise.) The Julian reform did not change , based on the Kalends, Nones and Ides, nor did it change the positions of these three dates within the months. Macrobius states that the extra days were added immediately before the last day of each month to avoid disturbing the position of the established religious ceremonies relative to the Nones and Ides of the month. However, since Roman dates after the Ides of the month counted down toward the start of the next month, the extra days had the effect of raising the initial value of the count of the day following the Ides in the lengthened months. Thus, in January, Sextilis and December the 14th day of the month became a.d. XIX Kal. instead of a.d. XVII Kal., while in April, June, September and November it became a.d. XVIII Kal. Romans of the time born after the Ides of a month responded differently to the effect of this change on their birthdays.
Mark Antony Marcus Antonius (14 January 1 August 30 BC), commonly known in English as Mark Antony, was a Ancient Rome, Roman politician and general who played a critical role in the Crisis of the Roman Republic, transformation of the Roman Republic f ...
kept his birthday on 14 January, which changed its date from a.d. XVII Kal. Feb to a.d. XIX Kal. Feb, a date that had previously not existed.
Livia Livia Drusilla (30 January 59 BC – 28 September 29 AD) was Roman empress from 27 BC to AD 14 as the wife of Roman emperor, Emperor Augustus. She was known as Julia Augusta after her formal Adoption in ancient Rome, adoption into the Julian fam ...

Livia
kept the date of her birthday unchanged at a.d. III Kal. Feb., which moved it from 28 to 30 January, a day that had previously not existed.
Augustus Caesar Augustus (23 September 63 BC19 August AD 14) was the first Roman emperor The Roman emperor was the ruler of the Roman Empire during the imperial period (starting in 27 BC). The emperors used a variety of different titles through ...

Augustus
kept his on 23 September, but both the old date (a.d. VIII Kal. Oct.) and the new (a.d. IX Kal. Oct.) were celebrated in some places. The inserted days were all initially characterised as ''dies fasti'' (F – see
Roman calendar The Roman calendar was the calendar A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A calendar date, date is the designation of a single, specific ...
). The character of a few festival days was changed. In the early Julio-Claudian period a large number of festivals were decreed to celebrate events of dynastic importance, which caused the character of the associated dates to be changed to NP. However, this practice was discontinued around the reign of
Claudius Claudius ( ; Tiberius Claudius Caesar Augustus Germanicus; 1 August 10 BC – 13 October AD 54) was the fourth Roman emperor The Roman emperor was the ruler of the Roman Empire during the History of the Roman Empire, imperial p ...

Claudius
, and the practice of characterising days fell into disuse around the end of the first century AD: the Antonine jurist
Gaius Gaius, sometimes spelled ''Gajus'', Cajus, Caius, was a common Latin praenomen The praenomen (; plural: praenomina) was a personal name A personal name, or full name, in onomastic Onomastics or onomatology is the study of the etymology, ...
speaks of ''dies nefasti'' as a thing of the past.


Intercalation

The old intercalary month was abolished. The new leap day was dated as ''ante diem bis sextum Kalendas Martias'' ('the sixth doubled day before the Kalends of March'), usually abbreviated as ''a.d. bis VI Kal. Mart.''; hence it is called in English the bissextile day. The year in which it occurred was termed ''annus bissextus'', in English the bissextile year. There is debate about the exact position of the bissextile day in the early Julian calendar. The earliest direct evidence is a statement of the 2nd century jurist
Celsus Celsus (; grc-x-hellen, Κέλσος, ''Kélsos''; ''fl.'' 175–177 CE) was a 2nd-century Greek philosopher Ancient Greek philosophy arose in the 6th century BC, at a time when the inhabitants of ancient Greece were struggling to repel ...
, who states that there were two-halves of a 48-hour day, and that the intercalated day was the "posterior" half. An inscription from AD 168 states that ''a.d. V Kal. Mart.'' was the day after the bissextile day. The 19th century chronologist argued that Celsus used the term "posterior" in a technical fashion to refer to the earlier of the two days, which requires the inscription to refer to the whole 48-hour day as the bissextile. Some later historians share this view. Others, following
Mommsen Mommsen is a surname, and may refer to one of a family of German historians, see Mommsen family: * Theodor Mommsen (1817–1903), classical scholar, winner of the Nobel Prize in Literature * Hans Mommsen (1930–2015), historian known for arguing ...

Mommsen
, take the view that Celsus was using the ordinary Latin (and English) meaning of "posterior". A third view is that neither half of the 48-hour "bis sextum" was originally formally designated as intercalated, but that the need to do so arose as the concept of a 48-hour day became obsolete. There is no doubt that the bissextile day eventually became the earlier of the two days for most purposes. In 238 Censorinus stated that it was inserted after the Terminalia (23 February) and was followed by the last five days of February, i.e., a.d. VI, V, IV, III and prid. Kal. Mart. (which would be 24 to 28 February in a common year and the 25th to 29th in a leap year). Hence he regarded the bissextum as the first half of the doubled day. All later writers, including Macrobius about 430,
Bede Bede ( ; ang, Bǣda , ; 672/326 May 735), also known as Saint Bede, The Venerable Bede, and Bede the Venerable ( la, Beda Venerabilis), was an English Benedictine The Benedictines, officially the Order of Saint Benedict ( la, Ordo Sa ...

Bede
in 725, and other medieval computists (calculators of Easter) followed this rule, as does the
liturgical calendar The liturgical year, also known as the church year or Christian year, as well as the kalendar, consists of the cycle of liturgical Liturgy is the customary public worship Worship is an act of religion, religious wikt:devotion, devotion u ...

liturgical calendar
of the Roman Catholic Church. However, Celsus' definition continued to be used for legal purposes. It was incorporated into Justinian's Digest, and in the English statute ''De anno et die bissextili'' of 1236, which was not formally repealed until 1879. The effect of the bissextile day on the
nundinal cycle The nundinae, sometimes anglicized to nundines,. were the market days of the ancient Roman calendar, forming a kind of weekend including, for a certain period, rest from work for the ruling class (Patrician (ancient Rome), Patricians). The n ...
is not discussed in the sources. According to Dio Cassius, a leap day was inserted in 41 BC to ensure that the first market day of 40 BC did not fall on 1 January, which implies that the old 8-day cycle was not immediately affected by the Julian reform. However, he also reports that in AD 44, and on some previous occasions, the market day was changed to avoid a conflict with a religious festival. This may indicate that a single nundinal letter was assigned to both halves of the 48-hour bissextile day by this time, so that the
RegifugiumThe Regifugium ("Flight of the King") or Fugalia ("Festival of the Flight") was an annual religious Religion is a social system, social-cultural system of designated religious behaviour, behaviors and practices, morality, morals, beliefs, worl ...
and the market day might fall on the same date but on different days. In any case, the 8-day nundinal cycle began to be displaced by the 7-day
week A week is a time unit equal to seven days. It is the standard time period used for cycles of rest days in most parts of the world, mostly alongside—although not strictly part of—the Gregorian calendar. In many languages, the days of the we ...
in the first century AD, and
dominical letterDominical letters or Sunday letters are a method used to determine the day of the week for particular dates. When using this method, each year is assigned a letter (or pair of letters for leap years) depending on which day of the week the year starts ...
s began to appear alongside nundinal letters in the fasti. During the late
Middle Ages In the history of Europe The history of Europe concerns itself with the discovery and collection, the study, organization and presentation and the interpretation of past events and affairs of the people of Europe since the beginning of ...
days in the month came to be numbered in consecutive day order. Consequently, the leap day was considered to be the last day in February in leap years, i.e., 29 February, which is its current position.


Sacrobosco's incorrect theory on month lengths

The Julian reform set the lengths of the months to their modern values. However, a different explanation for the lengths of Julian months, usually alleged to the 13th century scholar
Sacrobosco Johannes de Sacrobosco, also written Ioannis de Sacro Bosco, later called John of Holywood or John of Holybush ( 1195 – 1256), was a scholar, monk A monk (, from el, μοναχός, ''monachos'', "single, solitary" via Latin Latin (, ...
, but also attested in 12th century works, is still widely repeated, but is certainly wrong. Allegedly according to Sacrobosco, the month lengths for ordinary years in the Roman Republican calendar were a standard lunar calendar, similar the Greek city calendars. From Ianuarius to December, the month lengths were: : Sacrobosco then thought that Julius Caesar added one day to every month except Februarius, a total of 11 more days to regular months, giving the ordinary Julian year of 365 days. A single leap day could now be added to this extra-short Februarius: : He then said Augustus changed this, by taking one day from Februarius to add it to Sextilis, and then modifying the alternation of the following months, to: : so that the length of ''Augustus'' (August) would not be shorter than (and therefore inferior to) the length of ''Iulius'' (July), giving us the irregular month lengths which are still in use. Although plausible and filled with ingenious arithmetical organization, there is abundant evidence disproving this theory. First, the ''
Fasti Antiates Maiores The Fasti Antiates Maiores is a painted wall-calendar from the late Roman Republic, the oldest archaeologically attested local Roman calendar and the only such calendar known from before the Julian calendar, Julian calendar reforms. It was creat ...
'', a wall painting of a pre-Julian Roman calendar has survived. That pre-Julian calendar confirms the literary accounts that the months were already irregular before Julius Caesar reformed them, with an ordinary year of 355 days (not evenly divisible into Roman weeks), not 354, with month lengths arranged as: : Also, the Julian reform did not change the dates of the Nones and Ides. In particular, the Ides were late (on the 15th rather than 13th) in March, May, July, and October, showing that these months always had 31 days in the Roman calendar, whereas Sacrobosco's theory requires that March, May, and July were originally 30 days long and that the length of October was changed from 29 to 30 days by Caesar and to 31 days by Augustus. Further, Sacrobosco's theory is explicitly contradicted by the 3rd and 5th century authors Censorinus and Macrobius, and it is inconsistent with seasonal lengths given by Varro, writing in 37 BCE, before Sextilis was renamed for Augustus in 8 BCE, with the 31 day Sextilis given by an Egyptian papyrus from 24 BCE, and with the 28 day Februarius shown in the ''Fasti Caeretani'', which is dated before 12 BCE.


Year length; leap years

The Julian calendar has two types of year: "normal" years of 365 days and of 366 days. There is a simple cycle of three "normal" years followed by a leap year and this pattern repeats forever without exception. The Julian year is, therefore, on average 365.25 days long. Consequently, the Julian year drifts over time with respect to the tropical (solar) year (365.24217 days).Using value from Richards (2013, p. 587) for tropical year in mean solar days, the calculation is Although Greek astronomers had known, at least since
Hipparchus Hipparchus of Nicaea (; el, Ἵππαρχος, ''Hipparkhos'';  BC) was a Ancient Greek astronomy, Greek astronomer, geographer, and mathematician. He is considered the founder of trigonometry, but is most famous for his incidental discov ...
,
Claudius Ptolemy Claudius Ptolemy (; grc-koi, Κλαύδιος Πτολεμαῖος, ''Klaúdios Ptolemaîos'' ; la, Claudius Ptolemaeus; AD) was a mathematician A mathematician is someone who uses an extensive knowledge of mathematics Mathematics ...
, tr. G. J. Toomer, '' Ptolemy's Almagest'', 1998, Princeton University Press, p. 139. Hipparchus stated that the "solar year ... contains 365 days, plus a fraction which is less than by about th of the sum of one day and night".
a century before the Julian reform, that the tropical year was slightly shorter than 365.25 days, the calendar did not compensate for this difference. As a result, the calendar year gains about three days every four centuries compared to observed
equinox An equinox is traditionally defined as the time when the plane In mathematics, a plane is a flatness (mathematics), flat, two-dimensional surface (mathematics), surface that extends infinitely far. A plane is the two-dimensional space, two-di ...

equinox
times and the seasons. This discrepancy was largely corrected by the
Gregorian reform#REDIRECT Gregorian Reform : ''Should not be confused with the Gregorian calendar''. The Gregorian Reforms were a series of reforms initiated by Pope Gregory VII and the circle he formed in the Roman Curia, papal curia, c. 1050–80, which dealt w ...
of 1582. The Gregorian calendar has the same months and month lengths as the Julian calendar, but, in the Gregorian calendar, year numbers evenly divisible by 100 are not leap years, except that those evenly divisible by 400 remain leap years.Introduction to Calendars
(15 May 2013).
United States Naval Observatory The United States Naval Observatory (USNO) is one of the oldest scientific agencies in the United States The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a country Contiguous United Sta ...
.
(Even then, the Gregorian calendar diverges from astronomical observations by one day in 3,030 years.) The difference in the average length of the year between Julian (365.25 days) and Gregorian (365.2425 days) is 0.002%, making the Julian 10.8 minutes longer. The accumulated effect of this difference over some 1600 years since the basis for calculation of the date of Easter was determined at the First Council of Nicea means for example that, from 29 February ''Julian'' (13 March ''Gregorian'') 1900 and until 28 February ''Julian'' (13 March ''Gregorian'') 2100, the ''Julian'' calendar is 13 days behind the ''Gregorian'' calendar; one day after (i.e. on 29 February ''Julian'' or 14 March ''Gregorian''), the difference will be 14 days.


Leap year error

Although the new calendar was much simpler than the pre-Julian calendar, the pontifices initially added a leap day every three years, instead of every four. There are accounts of this in Solinus, Pliny, Ammianus, Suetonius, and Censorinus. Macrobius gives the following account of the introduction of the Julian calendar: So, according to Macrobius, # the year was considered to begin after the Terminalia (23 February), # the calendar was operated correctly from its introduction on 1 January 45 BC until the beginning of the fourth year (February 42 BC) at which point the priests inserted the first intercalation, # Caesar's intention was to make the first intercalation at the beginning of the fifth year (February 41 BC), # the priests made a further eleven intercalations after 42 BC at three-year intervals so that the twelfth intercalation fell in 9 BC, # had Caesar's intention been followed there would have been intercalations every four years after 41 BC, so that the ninth intercalation would have been in 9 BC, # after 9 BC, there were twelve years without
leap year A leap year (also known as an intercalary year or wikt:bissextile, bissextile year) is a calendar year that contains an additional day (or, in the case of a lunisolar calendar, a month) added to keep the calendar year synchronized with the astron ...

leap year
s, so that the leap days Caesar would have had in 5 BC, 1 BC and AD 4 were omitted and # after AD 4 the calendar was operated as Caesar intended, so that the next leap year was AD 8 and then leap years followed every fourth year thereafter. Some people have had different ideas as to how the leap years went. The above scheme is that of Scaliger (1583) in the table below. He established that the Augustan reform was instituted in AUC 746 (8 BC). The table below shows for each reconstruction the implied proleptic Julian date for the first day of Caesar's reformed calendar (Kal. Ian. AUC 709) and the first Julian date on which the Roman calendar date matches the Julian calendar after the completion of Augustus' reform. By the systems of Scaliger, Ideler and Bünting, the leap years prior to the suspension happen to be BC years that are divisible by 3, just as, after leap year resumption, they are the AD years divisible by 4. Pierre Brind'Amour argued that "only one day was intercalated between 1/1/45 and 1/1/40 (disregarding a momentary 'fiddling' in December of 41) to avoid the nundinum falling on Kal. Ian." Alexander Jones says that the correct Julian calendar was in use in Egypt in 24 BC, implying that the first day of the reform in both Egypt and Rome, , was the Julian date 1 January if 45 BC was a leap year and 2 January if it was not. This necessitates fourteen leap days up to and including AD 8 if 45 BC was a leap year and thirteen if it was not. In 1999, a papyrus was discovered which gives the dates of astronomical phenomena in 24 BC in both the Egyptian and Roman calendars. From , Egypt had two calendars: the old Egyptian in which every year had 365 days and the new Alexandrian in which every fourth year had 366 days. Up to the date in both calendars was the same. The dates in the Alexandrian and Julian calendars are in one-to-one correspondence except for the period from 29 August in the year preceding a Julian leap year to the following 24 February. From a comparison of the astronomical data with the Egyptian and Roman dates, Alexander JonesAlexander Jones, ''Calendrica II: Date Equations from the Reign of Augustus'', Zeitschrift fűr Papyrologie und Epigraphik 129 (2000) 159–166, available a

concluded that the Egyptian astronomers (as opposed to travellers from Rome) used the correct Julian calendar. Due to the confusion about this period, we cannot be sure exactly what day (e.g.
Julian day number The Julian day is the continuous count of days since the beginning of the Julian period, and is used primarily by astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field ou ...
) any particular Roman date refers to before March of 8 BC, except for those used in Egypt in 24BC which are secured by astronomy. An inscription has been discovered which orders a
new calendar Calendar reform or calendrical reform is any significant revision of a calendar system. The term sometimes is used instead for a proposal to switch to a different calendar design. Principles The prime objective of a calendar is to unambiguous ...
to be used in the
Province of Asia File:Asia minor roman power.jpg, 350px, The Roman conquest of Asia minor. The Roman province of Asia or Asiana ( el, Ἀσία or Ἀσιανή), in Byzantine Empire, Byzantine times called Phrygia, was an administrative unit added to the late R ...
to replace the previous Greek lunar calendar. According to one translation This is historically correct. It was decreed by the proconsul that the first day of the year in the new calendar shall be Augustus' birthday, a.d. IX Kal. Oct. Every month begins on the ninth day before the kalends. The date of introduction, the day after 14 Peritius, was 1 Dystrus, the next month. The month after that was Xanthicus. Thus Xanthicus began on a.d. IX Kal. Mart., and normally contained 31 days. In leap year, however, it contained an extra "Sebaste day", the Roman leap day, and thus had 32 days. From the lunar nature of the old calendar we can fix the starting date of the new one as 24 January, in the Julian calendar, which was a leap year. Thus from inception the dates of the reformed Asian calendar are in one-to-one correspondence with the Julian. Another translation of this inscription is This would move the starting date back three years to 8 BC, and from the lunar synchronism back to 26 January (Julian). But since the corresponding Roman date in the inscription is 24 January, this must be according to the incorrect calendar which in 8 BC Augustus had ordered to be corrected by the omission of leap days. As the authors of the previous paper point out, with the correct four-year cycle being used in Egypt and the three-year cycle abolished in Rome, it is unlikely that Augustus would have ordered the three-year cycle to be introduced in Asia.


Month names

The Julian reform did not immediately cause the names of any months to be changed. The old
intercalary month Intercalation or embolism in timekeeping is the insertion of a leap day, week, or month into some calendar years to make the calendar follow the seasons or moon phases. Lunisolar calendar A lunisolar calendar is a calendar in many culture Cul ...
was abolished and replaced with a single intercalary day at the same point (i.e., five days before the end of February). January continued to be the first month of the year. The Romans later renamed months after Julius Caesar and Augustus, renaming Quintilis as "Iulius" (July) in 44 BC and Sextilis as "Augustus" (August) in 8 BC. Quintilis was renamed to honour Caesar because it was the month of his birth. According to a ''
senatus consultum A ''senatus consultum'' (Latin – decree of the senate; plural ''senatus consulta'') is a text emanating from the senate in Ancient Rome. It is used in the modern phrase ''senatus consultum ultimum''. Translated into French as ''sénatus-cons ...
'' quoted by Macrobius, Sextilis was renamed to honour Augustus because several of the most significant events in his rise to power, culminating in the fall of Alexandria, occurred in that month. Other months were renamed by other emperors, but apparently none of the later changes survived their deaths. In AD 37,
Caligula Caligula (; 31 August 12 – 24 January 41 AD), formally known as Gaius (Gaius Gaius, sometimes spelled ''Gajus'', Cajus, Caius, was a common Latin praenomen The praenomen (; plural: praenomina) was a given name, personal name chosen by th ...

Caligula
renamed September as "Germanicus" after his
father A father is the male Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization. A male organism cannot sexual reprod ...

father
; in AD 65,
Nero Nero ( ; full name: Nero Claudius Caesar Augustus Germanicus; 15 December AD 37 – 9 June AD 68) was the fifth emperor of Rome. He was Adoption in Ancient Rome, adopted by the Roman emperor Claudius at the age of 13 and s ...

Nero
renamed April as "Neroneus", May as "Claudius" and June as "Germanicus"; and in AD 84
Domitian Domitian (; la, Domitianus; 24 October 51 – 18 September 96) was Roman emperor The Roman emperor was the ruler of the Roman Empire during the History of the Roman Empire, imperial period (starting in 27 BC). The emperors used a v ...

Domitian
renamed September as "Germanicus" and October as "Domitianus".
Commodus Commodus (; 31 August 161 – 31 December 192) was a Roman emperor The Roman emperor was the ruler of the Roman Empire The Roman Empire ( la, Imperium Rōmānum ; grc-gre, Βασιλεία τῶν Ῥωμαίων, Basileía tôn R ...

Commodus
was unique in renaming all twelve months after his own adopted names (January to December): "Amazonius", "Invictus", "Felix", "Pius", "Lucius", "Aelius", "Aurelius", "Commodus", "Augustus", "Herculeus", "Romanus", and "Exsuperatorius". The emperor
Tacitus Publius Cornelius Tacitus ( , ; – ) was a Roman historian and politician. Tacitus is widely regarded as one of the greatest Roman historians by modern scholars. He lived in what has been called the Silver Age of Latin literature Classi ...
is said to have ordered that September, the month of his birth and accession, be renamed after him, but the story is doubtful since he did not become emperor before November 275. Similar honorific month names were implemented in many of the provincial calendars that were aligned to the Julian calendar. Other name changes were proposed but were never implemented.
Tiberius Tiberius Caesar Augustus (; 16 November 42 BC – 16 March AD 37) was the second Roman emperor The Roman emperor was the ruler of the Roman Empire during the History of the Roman Empire, imperial period (starting in 27 BC). The emperors use ...

Tiberius
rejected a senatorial proposal to rename September as "Tiberius" and October as "Livius", after his mother Livia.
Antoninus Pius Antoninus Pius (; la, Antōnīnus Pius ; 19 September 86 – 7 March 161) was Roman emperor The Roman emperor was the ruler of the Roman Empire during the History of the Roman Empire, imperial period (starting in 27 BC). The emper ...

Antoninus Pius
rejected a senatorial decree renaming September as "Antoninus" and November as "Faustina", after his empress. Much more lasting than the ephemeral month names of the post-Augustan Roman emperors were the Old High German names introduced by
Charlemagne Charlemagne ( , ) or Charles the Great ( la, Carolus Magnus; 2 April 748 – 28 January 814) was King of the Franks The Franks—Germanic-speaking peoples that invaded the Western Roman Empire in the 5th century—were first led by i ...

Charlemagne
. According to his biographer, Charlemagne renamed all of the months agriculturally into German. These names were used until the 15th century, over 700 years after his rule, and continued, with some modifications, to see some use as "traditional" month names until the late 18th century. The names (January to December) were: ''Wintarmanoth'' ("winter month"), ''Hornung'',This name of February, the only name in the list without the "month" suffix, is explained by König, ''Festschrift Bergmann'' (1997), pp. 425 ff. as a collective of ''
horn Horn usually refers to: *Horn (acoustic), a conical or bell shaped aperture used to guide sound ** Horn (instrument), collective name for tube-shaped wind musical instruments *Horn (anatomy), a pointed, bony projection on the head of various anima ...
'', taken to refer to the antlers shed by
red deer The red deer (''Cervus elaphus'') is one of the largest deer Deer or true deer are ed s forming the Cervidae. The two main groups of deer are the , including the , the (wapiti), the , and the ; and the , including the (caribou), , th ...

red deer
during this time. Older explanations compare the name with Old Frisian ''horning'' (Anglo-Saxon ''hornung-sunu'', Old Norse ''hornungr'') meaning "bastard, illegitimate son", taken to imply a meaning of "disinherited" in reference to February being the shortest of months.
''Lentzinmanoth'' ("spring month", "
Lent Lent (Latin: ''Quadragesima'', 'Fortieth') is a Solemnity, solemn religious moveable feast#Lent, observance in the Christian liturgical calendar commemorating the Temptation of Jesus, 40 days Jesus spent fasting in the desert, according to the ...
month"), ''Ostarmanoth'' ("
Easter Easter,Traditional names for the feast in English are "Easter Day", as in the ''Book of Common Prayer''; "Easter Sunday", used by James Ussher''The Whole Works of the Most Rev. James Ussher, Volume 4'' and Samuel Pepys''The Diary of Samuel Pe ...
month"), ''Wonnemanoth'' ("
joy The word joy means the emotion evoked by well-being, success, or good fortune, and is typically associated with feelings of intense, long lasting happiness. Distinction vs similar states saw a clear distinction between joy, pleasure Ple ...
-month", a corruption of ''Winnimanoth'' "pasture-month"), ''Brachmanoth'' ("
fallow Fallow is a farming Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases in ...
-month"), ''Heuuimanoth'' ("hay month"), ''Aranmanoth'' (":wikt:earnian, reaping month"), ''Witumanoth'' ("wood month"), ''Windumemanoth'' ("vintage month"), ''Herbistmanoth'' ("harvest month"), and ''Heilagmanoth'' ("holy month"). The calendar month names used in western and northern Europe, in Byzantium, and by the Berber calendar#The months, Berbers, were derived from the Latin names. However, in eastern Europe older seasonal month names continued to be used into the 19th century, and in some cases are still in use, in many languages, including: Belarusian months, Belarusian, Bulgarian months, Bulgarian, Croatian months, Croatian, Czech months, Czech, Finnish, Georgian calendar, Georgian, Lithuanian calendar#Names of the months, Lithuanian, Macedonian months, Macedonian, Polish months, Polish, Romanian calendar#Traditional month names, Romanian, Slovene months, Slovene, Ukrainian months, Ukrainian. When the Ottoman Empire adopted the Julian calendar, in the form of the Rumi calendar, the Rumi calendar#History, month names reflected Ottoman tradition.


Year numbering

The principal method used by the Romans to identify a year for dating purposes was to name it after the two consuls who took office in it, the eponymous period in question being the consular year. Beginning in 153 BC, consuls began to take office on 1 January, thus synchronizing the commencement of the consular and calendar years. The calendar year has begun in January and ended in December since about 450 BC according to Ovid or since about 713 BC according to Macrobius and Plutarch (see
Roman calendar The Roman calendar was the calendar used by the Roman kingdom and Roman Republic, republic. The term often includes the Julian calendar established by the reforms of the Roman dictator, dictator Julius Caesar and Roman emperor, emperor August ...
). Julius Caesar did not change the beginning of either the consular year or the calendar year. In addition to consular years, the Romans sometimes used the regnal year of the emperor, and by the late 4th century documents were also being dated according to the 15 year cycle of the
indiction An indiction ( la, indictio, impost) was a periodic reassessment of taxation in the Roman Empire which took place every fifteen years. In Late Antiquity, this 15-year cycle began to be used to date documents and it continued to be used for this pu ...
. In 537, Justinian I, Justinian required that henceforth the date must include the name of the emperor and his regnal year, in addition to the indiction and the consul, while also allowing the use of local Calendar era, eras. In 309 and 310, and from time to time thereafter, no consuls were appointed. When this happened, the consular date was given a count of years since the last consul (called "post-consular" dating). After 541, only the reigning emperor held the consulate, typically for only one year in his reign, and so post-consular dating became the norm. Similar post-consular dates were also known in the west in the early 6th century. The system of consular dating, long obsolete, was formally abolished in the law code of Leo VI the Wise, Leo VI, issued in 888. Only rarely did the Romans number the year from the founding of Rome, founding of the city (of Rome), ''ab urbe condita'' (AUC). This method was used by Roman historians to determine the number of years from one event to another, not to date a year. Different historians had several different dates for the founding. The ''Fasti Capitolini'', an inscription containing an official list of the consuls which was published by Augustus, used an epoch (reference date), epoch of 752 BC. The epoch used by Marcus Terentius Varro, Varro, 753 BC, has been adopted by modern historians. Indeed, Renaissance editors often added it to the manuscripts that they published, giving the false impression that the Romans numbered their years. Most modern historians tacitly assume that it began on the day the consuls took office, and ancient documents such as the ''Fasti Capitolini'' which use other ab urbe condita, AUC systems do so in the same way. However, Censorinus, writing in the 3rd century AD, states that, in his time, the ab urbe condita, AUC year began with the Parilia, celebrated on 21 April, which was regarded as the actual anniversary of the foundation of Rome. Many local eras, such as the Era of Actium and the Spanish Era, were adopted for the Julian calendar or its local equivalent in the provinces and cities of the Roman Empire. Some of these were used for a considerable time. Perhaps the best known is the Era of Martyrs, sometimes also called ''Anno Diocletiani'' (after Diocletian), which was associated with the Alexandrian calendar and often used by the
Alexandria Alexandria ( or ; ar, الإسكندرية ; arz, اسكندرية ; Coptic language, Coptic: Rakodī; el, Αλεξάνδρεια ''Alexandria'') is the List of cities and towns in Egypt, third-largest city in Egypt after Cairo and Giza, ...

Alexandria
n Christians to number their Easters during the 4th and 5th centuries, and continues to be used by the Coptic and Ethiopian Orthodox Church, Ethiopian churches. In the eastern Mediterranean, the efforts of Christian chronographers such as Annianus of Alexandria to date the Biblical creation of the world led to the introduction of Anno Mundi eras based on this event. The most important of these was the Etos Kosmou, used throughout the Byzantine world from the 10th century and in Russia until 1700. In the west, the kingdoms succeeding the empire initially used indictions and regnal years, alone or in combination. The chronicler Prosper of Aquitaine, in the fifth century, used an era dated from the Passion (Christianity), Passion of Christ, but this era was not widely adopted. Dionysius Exiguus proposed the system of Anno Domini in 525. This era gradually spread through the western Christian world, once the system was adopted by
Bede Bede ( ; ang, Bǣda , ; 672/326 May 735), also known as Saint Bede, The Venerable Bede, and Bede the Venerable ( la, Beda Venerabilis), was an English Benedictine The Benedictines, officially the Order of Saint Benedict ( la, Ordo Sa ...

Bede
in the eighth century. The Julian calendar was also used in some Muslim countries. The
Rumi calendar The ''Rumi'' calendar ( tr, Rumi takvim, lit. "Roman calendar"), a specific calendar based on the Julian calendar was officially used by the Ottoman Empire after Tanzimat (1839) and by its successor, the Republic of Turkey until 1926. It was adopt ...
, the Julian calendar used in the later years of the Ottoman Empire, adopted an era derived from the lunar Islamic calendar, AH year equivalent to AD 1840, i.e., the effective Rumi calendar, Rumi epoch was AD 585. In recent years, some users of the Berber calendar#The computation of the years, Berber calendar have adopted an era starting in 950 BC, the approximate date that the Libyan pharaoh came to power in Egypt.


New Year's Day

The Roman calendar began the year on 1 January, and this remained the start of the year after the Julian reform. However, even after local calendars were aligned to the Julian calendar, they started the new year on different dates. The Alexandrian calendar in Egypt started on 29 August (30 August after an Alexandrian leap year). Several local provincial calendars were aligned to start on the birthday of Augustus, 23 September. The indiction caused the Byzantine Empire, Byzantine year, which used the Julian calendar, to begin on 1 September; this date is still used in the
Eastern Orthodox Church The Eastern Orthodox Church, also called the Orthodox Church, is the second-largest Christian church, with approximately 220 million baptised members. It operates as a communion Communion may refer to: Religion * The Eucharist (also cal ...
for the beginning of the liturgical year. When the Julian calendar was adopted in AD 988 by Vladimir I of Kiev, the year was numbered Anno Mundi 6496, beginning on 1 March, six months after the start of the Byzantine Anno Mundi year with the same number. In 1492 (AM 7000), Ivan III, according to church tradition, realigned the start of the year to 1 September, so that AM 7000 only lasted for six months in Russia, from 1 March to 31 August 1492. During the Middle Ages 1 January retained the name ''New Year's Day'' (or an equivalent name) in all western European countries (affiliated with the Roman Catholic Church), since the medieval calendar continued to display the months from January to December (in twelve columns containing 28 to 31 days each), just as the Romans had. However, most of those countries began their numbered year on 25 December (the Nativity of Jesus), 25 March (the Annunciation, Incarnation of Jesus), or even Easter, as in France (see the Liturgical year article for more details). In Anglo-Saxon England, the year most commonly began on 25 December, which, as (approximately) the
winter solstice The winter solstice, also called the hibernal solstice, occurs when either of Earth's geographical pole, poles reaches its maximum axial tilt, tilt away from the Sun. This happens twice yearly, once in each hemisphere (Northern Hemisphere, Nort ...

winter solstice
, had marked the start of the year in pagan times, though 25 March (the
equinox An equinox is traditionally defined as the time when the plane In mathematics, a plane is a flatness (mathematics), flat, two-dimensional surface (mathematics), surface that extends infinitely far. A plane is the two-dimensional space, two-di ...

equinox
) is occasionally documented in the 11th century. Sometimes the start of the year was reckoned as 24 September, the start of the so-called "western indiction" introduced by Bede. These practices changed after the Norman conquest. From 1087 to 1155 the English year began on 1 January, and from 1155 to 1751 it began on 25 March. In 1752 it was moved back to 1 January. (See Calendar (New Style) Act 1750). Even before 1752, 1 January was sometimes treated as the start of the new year – for example by Pepys – while the "year starting 25th March was called the Civil or Legal Year".Spathaky, Mik
Old Style and New Style dates and the change to the Gregorian calendar
To reduce misunderstandings on the date, it was not uncommon for a date between 1 January and 24 March to be written as "1661/62". This was to explain to the reader that the year was 1661 counting from March and 1662 counting from January as the start of the year.Spathaky, Mik

"An oblique stroke is by far the most usual indicator, but sometimes the alternative final figures of the year are written above and below a horizontal line, as in a fraction (a form which cannot easily be reproduced here in ASCII text). Very occasionally a hyphen is used, as 173334."
(For more detail, see Dual dating). Most western European countries shifted the first day of their numbered year to 1 January while they were still using the Julian calendar, ''before'' they adopted the Gregorian calendar, many during the 16th century. The following table shows the years in which various countries adopted 1 January as the start of the year. Eastern European countries, with populations showing allegiance to the orthodoxy, Orthodox Church, began the year on 1 September from about 988. The Rumi calendar used in the Ottoman Empire began the civil year on 1 March until 1918.


Replacement by the Gregorian calendar

The Julian calendar Adoption of the Gregorian calendar, has been replaced as the civil calendar by the
Gregorian calendar The Gregorian calendar is the used in most of the world. It was introduced in October 1582 by as a modification of the , reducing the average year from 365.25 days to 365.2425 days, and adjusting for the drift in the that the inaccuracy ha ...
in all countries which officially used it. Turkey switched (for fiscal purposes) on Dual Dating, 16 February/1 March 1917. Russia changed on 1/14 February 1918. Greece made the change for civil purposes on 16 February/1 March 1923, but the national day (25 March), was to remain on the old calendar. Most Christian denominations in the west and areas evangelised by western churches have made the change to Gregorian for their liturgical calendars to align with the civil calendar. A calendar similar to the Julian one, the Alexandrian calendar, is the basis for the Ethiopian calendar, which is still the civil calendar of Ethiopia. Egypt converted from the Alexandrian calendar to Gregorian on 1 Thaut 1592/11 September 1875. During the changeover between calendars and for some time afterwards, dual dating was used in documents and gave the date according to both systems. In contemporary as well as modern texts that describe events during the period of change, it is customary to clarify to which calendar a given date refers by using an Old Style and New Style dates, O.S. or N.S. suffix (denoting Old Style, Julian or New Style, Gregorian).


Transition history

The Julian calendar was in general use in Europe and northern Africa until 1582, when
Pope Gregory XIII Pope Gregory XIII ( la, Gregorius XIII; 7 January 1502 – 10 April 1585), born Ugo Boncompagni, was head of the Catholic Church The Catholic Church, also known as the Roman Catholic Church, is the , with 1.3 billion Catholics . ...

Pope Gregory XIII
promulgated the Gregorian calendar. Reform was required because too many leap days were added with respect to the astronomical seasons under the Julian scheme. On average, the astronomical solstices and the equinoxes advance by 10.8 minutes per year against the Julian year. As a result, 21 March (which is the base date for the Computus, calculating the date of Easter) gradually moved out of alignment with the March equinox. While Hipparchus and presumably Sosigenes of Alexandria, Sosigenes were aware of the discrepancy, although not of its correct value, it was evidently felt to be of little importance at the time of the Julian reform (46 BC). However, it accumulated significantly over time: the Julian calendar gained a day every 128 years. By 1582, 21 March was ten days out of alignment with the March equinox, the date where it supposedly had been in 325, the year of the First Council of Nicaea, Council of Nicaea. The Gregorian calendar was soon adopted by most Catholic countries (e.g., Spain, Portugal, Poland, most of Italy). Protestant countries followed later, and some countries of eastern Europe even later. In the British Empire (including the United States, American colonies), Wednesday was followed by Thursday . For 12 years from 1700 Sweden used a Swedish calendar, modified Julian calendar, and adopted the Gregorian calendar in 1753. Since the Julian and Gregorian calendars were long used simultaneously, although in different places, calendar dates in the transition period are often ambiguous, unless it is specified which calendar was being used. In some circumstances, double dates might be used, one in each calendar. The notation Old Style and New Style dates, "Old Style" (O.S.) is sometimes used to indicate a date in the Julian calendar, as opposed to Old Style and New Style dates, "New Style" (N.S.), which either represents the Julian date with the start of the year as 1 January or a full mapping onto the Gregorian calendar. This notation is used to clarify dates from countries that continued to use the Julian calendar after the Gregorian reform, such as Great Britain, which did not switch to the reformed calendar until 1752, or Russia, which did not switch until 1918 (see Soviet calendar). This is why the Russian Revolution of 7 November 1917 N.S. is known as the October Revolution, because it began on 25 October O.S. Throughout the long transition period, the Julian calendar has continued to diverge from the Gregorian. This has happened in whole-day steps, as leap days that were dropped in certain centennial years in the Gregorian calendar continued to be present in the Julian calendar. Thus, in the year 1700 the difference increased to 11 days; in 1800, 12; and in 1900, 13. Since 2000 was a leap year according to both the Julian and Gregorian calendars, the difference of 13 days did not change in that year: (Gregorian) fell on (Julian). This difference of 13 days will persist until Saturday 28 February 2100 (Julian), i.e. 13 March 2100 (Gregorian), since 2100 is ''not'' a Gregorian leap year, but ''is'' a Julian leap year; the next day the difference will be of 14 days: Sunday 29 February (Julian) will be Sunday 14 March (Gregorian); the next day Monday (Julian) falls on Monday (Gregorian).


Modern usage


Eastern Orthodox

Although most Eastern Orthodox Church, Eastern Orthodox countries (most of them in Eastern Europe, eastern or southeastern Europe) had adopted the Gregorian calendar by 1924, their national churches had not. The "Revised Julian calendar" was endorsed by a synod in Constantinople in May 1923, consisting of a solar part which was and will be identical to the Gregorian calendar until the year 2800, and a lunar part which calculated Easter astronomically at Jerusalem. All Orthodox churches refused to accept the lunar part, so all Orthodox churches continue to celebrate Easter according to the Julian calendar, with the exception of the Finnish Orthodox Church. (The Estonian Apostolic Orthodox Church, Estonian Orthodox Church was also an exception from 1923 to 1945.) The solar part of the Revised Julian calendar was accepted by only some Orthodox churches. Those that did accept it, with hope for improved dialogue and negotiations with the western denominations, were the Ecumenical Patriarchate of Constantinople, the Patriarchates of Greek Church of Alexandria, Alexandria, Eastern Orthodox Church of Antioch, Antioch, the Orthodox Churches of Church of Greece, Greece, Orthodox Church of Cyprus, Cyprus, Romanian Orthodox Church, Romania, Polish Orthodox Church, Poland (from 1924 to 2014; it is still permitted to use the Revised Julian calendar in parishes that want it), Bulgarian Orthodox Church, Bulgaria (in 1963), and the Orthodox Church in America (although some OCA parishes are permitted to use the Julian calendar). Thus these churches celebrate the Nativity of Jesus, Nativity on the same day that western Christians do, 25 December Gregorian until 2799. The Orthodox Churches of Eastern Orthodox Patriarchate of Jerusalem, Jerusalem, Russian Orthodox Church, Russia, Serbian Orthodox Church, Serbia, Montenegrin Orthodox Church, Montenegro, Poland (from 15 June 2014), Macedonian Orthodox Church – Ohrid Archbishopric, North Macedonia, Georgian Orthodox and Apostolic Church, Georgia, History of Christianity in Ukraine, Ukraine, and the Greek Old Calendarists and other groups continue to use the Julian calendar, thus they celebrate the Nativity on 25 December ''Julian'' (which is 7 January ''Gregorian'' until 2100). The Russian Orthodox Church has some parishes in the West that celebrate the Nativity on 25 December ''Gregorian'' until 2799. Parishes of the Orthodox Church in America Bulgarian Diocese, both before and after the 1976 transfer of that diocese from the Russian Orthodox Church Outside Russia to the Orthodox Church in America, were permitted to use this date. Some Old Calendarist groups which stand in opposition to the state churches of their homelands will use the Great Feast of the Epiphany (feast), Theophany (January 6 (Eastern Orthodox liturgics), 6 January ''Julian''/19 January ''Gregorian'') as a day for Crucession, religious processions and the Great Blessing of Waters, to publicise their cause.


Date of Easter

Most branches of the
Eastern Orthodox Church The Eastern Orthodox Church, also called the Orthodox Church, is the second-largest Christian church, with approximately 220 million baptised members. It operates as a communion Communion may refer to: Religion * The Eucharist (also cal ...
use the Julian calendar for Computus, calculating the date of Easter, upon which the timing of all the other moveable feasts depends. Some such churches have adopted the Revised Julian calendar for the observance of fixed feasts, while such Orthodox churches retain the Julian calendar for all purposes.


Syriac Christianity

The Ancient Assyrian Church of the East, an East Syriac rite that is commonly miscategorised under "eastern Orthodox", uses the Julian calendar, where its participants celebrate Christmas on 7 January ''Gregorian'' (which is 25 December ''Julian''). The Assyrian Church of the East, the church it split from in 1968 (the replacement of traditional Julian calendar with Gregorian calendar being among the reasons), uses the Gregorian calendar ever since the year of the schism. The Syriac Orthodox Church uses both Julian calendar and Gregorian calendar based on their regions and traditions they adapted.


Oriental Orthodox

The Oriental Orthodox Churches generally use the local calendar of their homelands. However, when calculating the Nativity Feast, most observe the Julian calendar. This was traditionally for the sake of unity throughout Christendom. In the west, some Oriental Orthodox Churches either use the Gregorian calendar or are permitted to observe the Nativity according to it. The Armenian Patriarchate of Jerusalem of Armenian Apostolic Orthodox Church uses Julian calendar, while the rest of Armenian Church uses Gregorian calendar. Both celebrate the Nativity as part of the Feast of Epiphany (holiday), Theophany according to their respective calendar.


Berbers

The Julian calendar is still used by the
Berbers Berbers or ''Imazighen'' ( ber, translit=Imaziɣen, ⵉⵎⴰⵣⵉⵖⵏ, ⵎⵣⵗⵏ; singular: , ) are an ethnic group mostly concentrated in North Africa, specifically Morocco, Algeria, Tunisia, Libya, the Canary Islands, and to a lesser ...

Berbers
of the Maghreb in the form of the Berber calendar.


See also

* Byzantine calendar * Conversion between Julian and Gregorian calendars * Julian day * Julian year (astronomy) * List of adoption dates of the Gregorian calendar per country * Mixed-style date * Old New Year * Proleptic Gregorian calendar * Proleptic Julian calendar * Revised Julian calendar * Roman timekeeping * Week


Footnotes


References


Bibliography

* Bonnie Blackburn and Leofranc Holford-Strevens, ''The Oxford Companion to the Year'', Oxford University Press, reprinted with corrections 2003. * * * * * * * * *


External links


Calendars through the ages
on WebExhibits.






Calendar Converter
– converts between several calendars, for example Gregorian, Julian, Mayan, Persian, Hebrew {{Authority control Julian calendar, Roman calendar Eastern Orthodox liturgy Liturgical calendars