TheInfoList

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 day within such a system. A calendar is also ...

used by the
Roman kingdom The Roman Kingdom, also referred to as the Roman monarchy, or the regal period of ancient Rome, was the earliest period of Roman history The history of Rome includes the history of the Rome, city of Rome as well as the Ancient Rome, civili ...
and
republic A republic () is a form of government A government is the system or group of people governing an organized community, generally a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a month ...
. The term often includes the
Julian calendar 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 B ...
established by the reforms of the
dictator A dictator is a political leader who possesses absolute power. A dictatorship A dictatorship is a form of government A government is the system or group of people governing an organized community, generally a state. In the ...
Julius Caesar Gaius Julius Caesar (; 12 July 100 BC – 15 March 44 BC) was a Roman Roman or Romans most often refers to: *, the capital city of Italy *, Roman civilization from 8th century BC to 5th century AD *, the people of ancient Rome *', shortened ...

and
emperor An emperor (from la, imperator The Latin word "imperator" derives from the stem of the verb la, imperare, label=none, meaning 'to order, to command'. It was originally employed as a title roughly equivalent to ''commander'' under the Roma ...
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 ...

in the late 1stcenturyBC and sometimes includes any system dated by
inclusive counting Counting is the process of determining the number A number is a mathematical object used to counting, count, measurement, measure, and nominal number, label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be ...
towards months'
kalends The calends or kalends ( la, kalendae) is the first day of every month in 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 b ...
, nones, and ides in the Roman manner. The term usually excludes the Alexandrian calendar of
Roman Egypt , conventional_long_name = Roman Egypt , common_name = Egypt , subdivision = Roman province, Province , nation = the Roman Empire , era = Late antiquity , capital = Alexandria , title_leader = Praefectus Augustalis , image_ ...

, which continued the unique months of that land's former calendar; the
Byzantine calendar The Byzantine calendar, also called "Creation Era of Constantinople" or "Era of the World" ( grc, Ἔτη Γενέσεως Κόσμου κατὰ Ῥωμαίους, also or , abbreviated as ε.Κ.; literal translation of ancient Greek "Roman ye ...
of the , which usually dated the Roman months in the simple count of the
ancient Greek calendar Ancient history is the aggregate of past eventsWordNet Search – 3.0
"History"
from t ...
s; and the
Gregorian calendar The Gregorian calendar is 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, speci ...
, which refined the Julian system to bring it into still closer alignment with the
tropical year A tropical year (also known as a solar year or tropical period) is the time Time is the continued sequence of existence and event (philosophy), events that occurs in an apparently irreversible process, irreversible succession from the past ...
. Roman dates were counted inclusively forward to the next of three principal days: the first of the month (the kalends), a day shortly before the middle of the month (the ides), and eight days—nine, counting inclusively—before this (the nones). The original calendar consisted of ten months beginning in spring with
March March is the third month of the year in both the Julian and Gregorian calendar The Gregorian calendar is the calendar A calendar is a system of organizing days. This is done by giving names to periods of time, typically days ...

; winter was left as an unassigned span of days. These months ran for 38 nundinal cycles, each forming an eight-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 ...

(nine days counted inclusively, hence the name) ended by religious rituals and a public market. The winter period was later divided into two months,
January January is the first month of the year in the Julian calendar, Julian and Gregorian calendars and the first of seven months to have a length of 31 days. The first day of the month is known as New Year's Day. It is, on average, the coldest mon ...
and
February February is the second month of the year in the Julian calendar, Julian and Gregorian calendars. The month has 28 days in common years or 29 in leap years, with the 29th day being called the ''leap day''. It is the first of five months not to ...
. The legendary early kings
Romulus Romulus () was the legendary founder Founder or Founders may refer to: Places *Founders Park, a stadium in South Carolina, formerly known as Carolina Stadium * Founders Park, a waterside park in Islamorada, Florida#In popular culture, Islamora ...
and
Numa Pompilius Numa Pompilius (; 753–673 BC; reigned 715–673 BC) was the legendary second king of Rome The king of Rome ( la, rex Romae) was the chief magistrate Chief magistrate is a public official, executive or judicial, whose office is the highest ...

were traditionally credited with establishing this early fixed calendar, which bears traces of its origin as an observational lunar one. In particular, the kalends, nones, and ides seem to have derived from the first sighting of the crescent moon, the
first-quarter moon The lunar phase or Moon phase is the shape of the Moon's directly sunlit portion as viewed from Earth. The lunar phases gradually change over a Orbital_period#Synodic_period, synodic month (about 29.53 days) as the Moon's orbital positions aro ...
, and the
full moon The full moon is the lunar phase s in 2022 as viewed from the Southern Hemisphere The Southern Hemisphere is the half (hemisphere Hemisphere may refer to: * A half of a sphere As half of the Earth * A hemispheres of Earth, hemisphere o ...

respectively. The system ran well short of the solar year, and it needed constant intercalation to keep religious festivals and other activities in their proper
season A season is a division of the year based on changes in weather Weather is the state of the atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or ...

s. This is a typical element of
lunisolar calendar A lunisolar 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 ...
s. For superstitious reasons, such intercalation occurred within the month of February even after it was no longer considered the last month. After the establishment of the Roman Republic, years began to be dated by consulships and control over intercalation was granted to 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 ...
, who eventually abused their power by lengthening years controlled by their political allies and shortening the years in their rivals' terms of office. Having won with
Pompey Gnaeus Pompeius Magnus (; 29 September 106 BC – 28 September 48 BC), known in English as Pompey or Pompey the Great, was a leading Roman Roman or Romans most often refers to: *, the capital city of Italy *, Roman civilization f ...

, Caesar used his position as Rome's chief pontiff to enact a
calendar reform 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 unambiguou ...
in 46BC, coincidentally making the year of his third consulship last for 446days. In order to avoid interfering with Rome's religious ceremonies, the reform added all its days towards the ends of months and did not adjust any nones or ides, even in months which came to have 31days. The Julian calendar was supposed to have a single
leap day February 29, also known as leap day or leap year day, is a date added to 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 ...
on 24 February (a doubled or ) every fourth year, but following Caesar's assassination the priests figured this using inclusive counting and mistakenly added this bissextile () day every three years. In order to bring the calendar back to its proper place, Augustus was obliged to suspend intercalation for one or two decades. The revised calendar remained slightly longer than the solar year; by the 16th century the date of
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 ...

had shifted so far away from the vernal equinox that
Pope Gregory XIII Pope Gregory XIII ( la, Gregorius XIII; it, Gregorio XIII; 7 January 1502 – 10 April 1585), born Ugo Boncompagni, was head of the Catholic Church and ruler of the Papal States from May 13th, 1572 to his death in 1585. He is best known for com ...
ordered the calendar's adjustment, resulting in the Gregorian calendar.

# History

## Prehistoric lunar calendar

The original Roman
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 within such a system. A calendar is also ...

is believed to have been an observational
lunar calendar A lunar 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 ...
whose months began from the first signs of a new crescent moon. Because a
lunar cycle The lunar phase or Moon phase is the shape of the Moon The Moon is Earth's only natural satellite. At about one-quarter the diameter of Earth (comparable to the width of Australia (continent), Australia), it is the largest natural s ...
is about days long, such months would have varied between . Twelve such months would have fallen short of the
solar year A tropical year (also known as a solar year or tropical period) is the time Time is the continued sequence of existence and event (philosophy), events that occurs in an apparently irreversible process, irreversible succession from the past ...
; without adjustment, such a year would have quickly rotated out of alignment with the seasons in the manner of the
Islamic calendar The Hijri calendar ( ar, ٱلتَّقْوِيم ٱلْهِجْرِيّ '), also known as the Lunar Hijri calendar and (in English) as the Islamic, Muslim or Arabic calendar, is a lunar calendar consisting of 12 lunar months in a year of 354 o ...
. Given the seasonal aspects of the later calendar and its associated religious festivals, this was presumably avoided through some form of intercalation or the suspension of the calendar during winter. Rome's 8-day week, 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 ...
, was shared with the
Etruscans The Etruscan civilization () of ancient Italy The history of Italy covers the Ancient Period, the Middle Ages and the modern era. Since classical times, ancient Phoenicians, Magna Graecia, Greeks, Etruscan civilization, Etruscans, and Celts ha ...

, who used it as the schedule of royal audiences. It was presumably a part of the early calendar and was credited in
Roman legend Roman mythology is the body of myths of ancient Rome as represented in the Latin literature, literature and Roman art, visual arts of the Romans. One of a wide variety of genres of Roman folklore, ''Roman mythology'' may also refer to the moder ...
variously to
Romulus Romulus () was the legendary founder Founder or Founders may refer to: Places *Founders Park, a stadium in South Carolina, formerly known as Carolina Stadium * Founders Park, a waterside park in Islamorada, Florida#In popular culture, Islamora ...
and
Servius Tullius Servius Tullius was the legendary sixth king of Rome The king of Rome ( la, rex Romae) was the chief magistrate Chief magistrate is a public official, executive or judicial, whose office is the highest in its class. Historically, the two d ...
.

## Legendary 10 month calendar

The Romans themselves described their first organized year as one with ten fixed months, each of . Such a decimal division fitted general Roman practice. The four 31 day months were called "full" (') and the others "hollow" (').. Its 304 days made up exactly 38
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 ...
s. The system is usually said to have left the remaining 50 odd days of the year as an unorganized "winter", although
Licinius Macer Gaius Licinius Macer (died 66BC) was an official and annalists, annalist of ancient Rome. Life A member of the ancient plebeian gens (Roman), clan Licinia (gens), Licinia, he was tribune in 73BC. Sallust mentions him agitating for the people's righ ...
's lost history apparently stated the earliest Roman calendar employed intercalation instead 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 Late antiquity is a periodization Periodization is the process or study ...

claims the 10 month calendar was allowed to shift until the summer and winter months were completely misplaced, at which time additional days belonging to no month were simply inserted into the calendar until it seemed things were restored to their proper place. Later Roman writers credited this calendar to
Romulus Romulus () was the legendary founder Founder or Founders may refer to: Places *Founders Park, a stadium in South Carolina, formerly known as Carolina Stadium * Founders Park, a waterside park in Islamorada, Florida#In popular culture, Islamora ...
, their legendary first king and
culture hero A culture hero is a mythological Myth is a consisting of s that play a fundamental role in a society, such as foundational tales or s. The main characters in myths are usually non-humans, such as , s, and other figures., and , eds. 2003. "M ...
, although this was common with other practices and traditions whose origin had been lost to them. Some scholars doubt the existence of this calendar at all, as it is only attested in late Republican and Imperial sources and supported only by the misplaced names of the months from September to December.. Rüpke also finds the coincidence of the length of the supposed "Romulan" year with the length of the first ten months of the Julian calendar to be suspicious.
Other traditions existed alongside this one, however.
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 ...

's ''
Parallel Lives 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 a ...
'' recounts that
Romulus Romulus () was the legendary founder Founder or Founders may refer to: Places *Founders Park, a stadium in South Carolina, formerly known as Carolina Stadium * Founders Park, a waterside park in Islamorada, Florida#In popular culture, Islamora ...
's calendar had been solar but adhered to the general principle that the year should last for 360 days. Months were employed secondarily and haphazardly, with some counted as 20 days and others as 35 or more.

## Republican calendar

The attested calendar of the
Roman Republic The Roman Republic ( la, Rēs pūblica Rōmāna ) was a state of the classical Roman civilization, run through public In public relations Public relations (PR) is the practice of managing and disseminating information from an indiv ...
was quite different. It followed Greek calendars in assuming a
lunar cycle The lunar phase or Moon phase is the shape of the Moon The Moon is Earth's only natural satellite. At about one-quarter the diameter of Earth (comparable to the width of Australia (continent), Australia), it is the largest natural s ...
of days and a
solar year A tropical year (also known as a solar year or tropical period) is the time Time is the continued sequence of existence and event (philosophy), events that occurs in an apparently irreversible process, irreversible succession from the past ...
of
synodic month In lunar calendar A lunar 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 sing ...
s ( days), which align every fourth year after the addition of two intercalary months. Two months were added at the end of the year to complete the cycle during winter,
January January is the first month of the year in the Julian calendar, Julian and Gregorian calendars and the first of seven months to have a length of 31 days. The first day of the month is known as New Year's Day. It is, on average, the coldest mon ...
and
February February is the second month of the year in the Julian calendar, Julian and Gregorian calendars. The month has 28 days in common years or 29 in leap years, with the 29th day being called the ''leap day''. It is the first of five months not to ...
, before the intercalary month inserted every two years; the intercalary month was sometimes known as
MercedoniusMercedonius (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 Repub ...
. The inequality between the lunar year of 355 days and the
tropical year A tropical year (also known as a solar year or tropical period) is the time Time is the continued sequence of existence and event (philosophy), events that occurs in an apparently irreversible process, irreversible succession from the past ...
of days led to a shortfall over four years of ( × 4) = 41 days. Theoretically, 22 days were interpolated into the calendar in the second year of the four-year cycle and 23 days in the fourth. This produced an excess of four days over the four years in line with the normal one day excess over one year. The method of correction was to truncate February by five days and follow it with the which thus commenced (normally) on the day after 23 February and had either 27 or 28 days. It did not acquire the alternative name Mercedonius until post-classical times. 23 February was the Terminalia and in a normal year it was ' Thus the dates of the festivals of the last five days of February were preserved on account of them being actually named and counted inclusively in days before the calends of March; they were traditionally part of the celebration for the new year. There was occasionally a delay of one day (a being inserted between 23 February and the start of the ) for the purpose of avoiding a clash between a particular festival and a particular day of the week (see for another example). The Roman superstitions concerning the numbering and order of the months seem to have arisen from
Pythagorean Pythagorean, meaning of or pertaining to the ancient Ionian mathematician, philosopher, and music theorist Pythagoras Pythagoras of Samos, or simply ; in Ionian Greek () was an ancient Ionians, Ionian Ancient Greek philosophy, Greek philos ...
superstitions concerning the luckiness of
odd number In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). I ...
s.. These Pythagorean-based changes to the Roman calendar were generally credited by the Romans to
Numa Pompilius Numa Pompilius (; 753–673 BC; reigned 715–673 BC) was the legendary second king of Rome The king of Rome ( la, rex Romae) was the chief magistrate Chief magistrate is a public official, executive or judicial, whose office is the highest ...

,
Romulus Romulus () was the legendary founder Founder or Founders may refer to: Places *Founders Park, a stadium in South Carolina, formerly known as Carolina Stadium * Founders Park, a waterside park in Islamorada, Florida#In popular culture, Islamora ...
's successor and the second of Rome's seven kings, as were the two new months of the calendar. Most sources thought he had established intercalation with the rest of his calendar. Although
Livy Titus Livius (; 59 BC – AD 17), known in English as Livy ( ), was a Ancient Rome, Roman historian. He wrote a monumental history of Rome and the Roman people, titled , covering the period from the earliest legends of Rome before the traditiona ...
's Numa instituted a ''lunar'' calendar, the author claimed the king had instituted a 19-year system of intercalation equivalent to the
Metonic cycle For example, by the 19-year Metonic cycle, the full moon repeats on or near Christmas day between 1711 and 2300. A small horizontal libration is visible comparing their appearances. A red color shows full moons that are also lunar eclipses. The ...

centuries before its development by Babylonian and Greek astronomers.
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 ...

's account claims he ended the former chaos of the calendar by employing 12months totalling 354days—the length of the
lunar Lunar most commonly means "of or relating to the Moon". Lunar may also refer to: Arts and entertainment * Lunar (series), ''Lunar'' (series), a series of video games * Lunar (song), "Lunar" (song), by David Guetta * "Lunar", a song by Priestess f ...
and Greek years—and biennial intercalary months of 22days. According to Livy's
Periochae The book ''History of Rome'', sometimes referred to as ''Ab Urbe Condita Libri'' (''Books from the Founding of the City''), is a monumental history of ancient Rome, written in Latin Latin (, or , ) is a classical language belonging to the ...
, the beginning of the consular year changed from March to January1 in 153BC to respond to a rebellion in Hispania. Plutarch believed Numa was responsible for placing January and February first in the calendar;
Ovid Pūblius Ovidius Nāsō (; 20 March 43 BC – 17/18 AD), known in English as Ovid ( ), was a Augustan literature (ancient Rome), Roman poet who lived during the reign of Augustus. He was a contemporary of the older Virgil and Horace, with whom ...

states January began as the first month and February the last, with its present order owing to the
Decemvirs The decemviri or decemvirs (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 ...
.
W. Warde Fowler William Warde Fowler (16 May 1847 – 15 June 1921) was an English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medie ...
believed the Roman priests continued to treat January and February as the last months of the calendar throughout the Republican period. According to the later writers Censorinus and Macrobius, to correct the mismatch of the correspondence between months and seasons due to the excess of one day of the Roman average year over the tropical year, the insertion of the intercalary month was modified according to the scheme: common year (355 days), leap year with 23-day February followed by 27-day Mercedonius (377 days), common year, leap year with 23-day February followed by 28-day Mercedonius (378 days), and so on for the first 16 years of a 24-year cycle. In the last 8 years, the intercalation took place with the month of Mercedonius only 27 days, except the last intercalation which did not happen. Hence, there would be a typical common year followed by a leap year of 377 days for the next 6 years and the remaining 2 years would sequentially be common years. The result of this twenty-four-year pattern was of great precision for the time: 365.25 days, as shown by the following calculation: $\frac=\frac=365.25$ The consuls' terms of office were not always a modern calendar year, but ordinary consuls were elected or appointed annually. The traditional
list of Roman consuls This is a list of Roman consul, consuls known to have held office, from the beginning of the Roman Republic to the latest use of the title in Roman Empire, Imperial times, together with those magistrates of the Republic who were appointed in plac ...
used by the Romans to date their years began in 509BC..

## Flavian reform

Gnaeus Flavius, a secretary (''scriba'') to censor App. Claudius Caecus, introduced a series of reforms in 304BC. Their exact nature is uncertain, although he is thought to have begun the custom of publishing the calendar in advance of the month, depriving the priests of some of their power but allowing for a more consistent calendar for official business.

## Julian reform

Julius Caesar Gaius Julius Caesar (; 12 July 100 BC – 15 March 44 BC) was a Roman Roman or Romans most often refers to: *, the capital city of Italy *, Roman civilization from 8th century BC to 5th century AD *, the people of ancient Rome *', shortened ...

, following his
victory The term victory (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 pow ...
in and in his role as ''
pontifex maximus The (Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in relation w ...
'', ordered a reformation of the calendar in 46BC. This was undertaken by a group of scholars apparently including 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, ...

n Sosigenes and the Roman M. Flavius. Its main lines involved the insertion of ten additional days throughout the calendar and regular intercalation of a single
leap day February 29, also known as leap day or leap year day, is a date added to 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 ...
every fourth year to bring the Roman calendar into close agreement with the solar year. The year 46BC was the last of the old system and included 3 intercalary months, the first inserted in February and two more—' and '—before the kalends of December.

## Later reforms

After Caesar's assassination,
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 ...
had Caesar's birth month Quintilis renamed
July July is the seventh month of the year (between June June is the sixth month of the year in the Julian calendar, Julian and Gregorian calendars, the second of four months to have a length of 30 days, and the third of five months to have ...
(') in his honor. After Antony's defeat at Actium,
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 ...

assumed control of Rome and, finding the priests had (owing to their inclusive counting) been intercalating every third year instead of every fourth, suspended the addition of leap days to the calendar for one or two decades until its proper position had been restored. See Julian calendar: Leap year error. In 8BC, the
plebiscite A referendum (plural: referendums or less commonly referenda) is a direct Direct may refer to: Mathematics * Directed set In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number th ...
''Lex Pacuvia de Mense Augusto'' renamed Sextilis
August August is the eighth month of the year in the Julian and Gregorian calendar The Gregorian calendar is the calendar A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, ...
(') in his honor. In large part, this calendar continued unchanged under 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 ...

. (
Egypt Egypt ( ar, مِصر, Miṣr), officially the Arab Republic of Egypt, is a transcontinental country This is a list of countries located on more than one continent A continent is one of several large landmasses. Generally identi ...

ians used the related Alexandrian calendar, which Augustus had adapted from their wandering ancient calendar to maintain its alignment with Rome's.) A few emperors altered the names of the months after themselves or their family, but such changes were abandoned by their successors.
Diocletian Diocletian (; la, Gaius Aurelius Valerius Diocletianus; born Diocles; 22 December c. 244 – 3 December 311) was from 284 to 305. Born to a family of low status in , Diocletian rose through the ranks of the military to become a commander of ...
began the 15-year
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 ...
census A census is the procedure of systematically calculating, acquiring and recording information Information is processed, organised and structured data Data (; ) are individual facts, statistics, or items of information, often numeric. In ...
; these became the required format for official dating under
Justinian Justinian I (; la, Flavius Petrus Sabbatius Iustinianus; grc-gre, Ἰουστινιανός ; 48214 November 565), also known as Justinian the Great, was the Byzantine emperor This is a list of the Byzantine emperors from the foundation o ...
.
Constantine Constantine most often refers to: * Constantine the Great Constantine I ( la, Flavius Valerius Constantinus; ; 27 February 22 May 337), also known as Constantine the Great, was a Roman emperor from 306 to 337. Born in Naissus, Dacia Mediterra ...

formally established 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 ...

by making
Sunday Sunday is the day of the week between Saturday and Monday. In most Western countries, Sunday is a day of rest and a part of the Workweek and weekend, weekend, whereas in much of the rest of the world, it is considered the first day of the week. ...

an official holiday in 321. Consular dating became obsolete following the abandonment of appointing nonimperial consuls in AD541. The Roman method of numbering the days of the month never became widespread in the Hellenized eastern provinces and was eventually abandoned by the
Byzantine Empire The Byzantine Empire, also referred to as the Eastern Roman Empire, or Byzantium, was the continuation of the Roman Empire The Roman Empire ( la, Imperium Rōmānum ; grc-gre, Βασιλεία τῶν Ῥωμαίων, Basileía tôn ...

in its calendar.

# Days

Roman dates were counted inclusively forward to the next one of three principal days within each month: *
Kalends The calends or kalends ( la, kalendae) is the first day of every month in 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 b ...
(' or '), the 1st day of each month. * Nones (' or '), the 7thday of full months and 5thday of hollow ones, 8days—"nine" by Roman reckoning—before the Ides in every month * Ides (', variously ' or '), the 15thday of full months and the 13thday of hollow ones, one day earlier than the middle of each month. These are thought to reflect a prehistoric lunar calendar, with the kalends proclaimed after the sighting of the first sliver of the new crescent moon a day or two after the
new moon In 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 ...

, the nones occurring on the day of the
first-quarter moon The lunar phase or Moon phase is the shape of the Moon's directly sunlit portion as viewed from Earth. The lunar phases gradually change over a Orbital_period#Synodic_period, synodic month (about 29.53 days) as the Moon's orbital positions aro ...
, and the ides on the day of the
full moon The full moon is the lunar phase s in 2022 as viewed from the Southern Hemisphere The Southern Hemisphere is the half (hemisphere Hemisphere may refer to: * A half of a sphere As half of the Earth * A hemispheres of Earth, hemisphere o ...

. The kalends of each month were sacred to
Juno Juno commonly refers to: *Juno (mythology), the Roman goddess of marriage and queen of the gods *Juno (film), ''Juno'' (film), 2007 Juno may also refer to: Arts, entertainment and media Fictional characters *Juno, in the film ''Jenny, Juno'' *Jun ...
and the ides to
Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
. The day before each was known as its eve ('); the day after each (') was considered particularly unlucky. The days of the month were expressed in early Latin using the ablative of time, denoting points in time, in the contracted form "the 6thDecember Kalends" ('). In classical Latin, this use continued for the three principal days of the month. but other days were idiomatically expressed in the
accusative case The accusative case (abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full version of the word or phras ...
, which usually expressed a duration of time, and took the form "6th day before the December Kalends" ('). This anomaly may have followed the treatment of days in
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
, reflecting the increasing use of such date phrases as an absolute phrase able to function as the object of another preposition,. or simply originated in a mistaken agreement of ' with the preposition ' once it moved to the beginning of the expression. In
late Latin Late Latin ( la, Latinitas serior) is the scholarly name for the written Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, kn ...
, this idiom was sometimes abandoned in favor of again using the ablative of time. The kalends were the day for payment of debts and the account books (') kept for them gave English its word ''
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 within such a system. A calendar is also ...

''. The public Roman calendars were the ''
fasti In ancient Rome In historiography Historiography is the study of the methods of historian ( 484– 425 BC) was a Greek historian who lived in the 5th century BC and one of the earliest historians whose work survives. A historian i ...
'', which designated the religious and legal character of each month's days. The Romans marked each day of such calendars with the letters: * F ('' fastus'', "permissible") on days when it was legal to initiate action in the courts of civil law (', "allowed days") * C (''comitialis'') on ''fasti'' days during which the Roman people could hold assemblies (') * N (''
nefastus The vocabulary of ancient Roman religion Religion in ancient Rome includes the ethnic religion of Ancient Rome that the ancient Romans, Romans used to define themselves as a people, as well as the religious practices of peoples brought unde ...
'') on days when political and judicial activities were prohibited (') * NP (uncertain) on public holidays ('''') * QRCF (uncertain) on days when the "king" (''
rex sacrorum In ancient Roman religion, the ''rex sacrorum'' ("king of the sacred", also sometimes ''rex sacrificulus'') was a senatorial priesthood reserved for patricians. Although in the historical era, the ''pontifex maximus The (Latin Latin (, ...
'') could convene an assembly * EN (', an archaic form of ', "halved") on days when most political and religious activities were prohibited in the morning and evening due to
sacrifices Sacrifice is the offering of food, objects or the lives of animals or humans to a higher purpose, in particular divine beings, as an act of propitiation or worship. Evidence of ritual animal sacrifice has been seen at least ancient Hebrew and ...

being prepared or offered but were acceptable for a period in the middle of the day Each day was also marked by a letter from A to H to indicate its place within 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 ...
of market days.

# Weeks

The
nundinae The nundinae, sometimes anglicized Linguistic anglicisation (or anglicization, occasionally anglification, anglifying, or Englishing) is the practice of modifying foreign words, names, and phrases to make them easier to spell, pronounce, o ...
were the market days which formed a kind of
weekend The workweek and weekend are the complementary parts of the 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 par ...
in
Rome , established_title = Founded , established_date = 753 BC , founder = King Romulus , image_map = Map of comune of Rome (metropolitan city of Capital Rome, region Lazio, Italy).svg , map_caption = The te ...
,
Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repubblica Italiana, links=no ), is a country consisting of a peninsula delimited by the Alps The Alps ; german: Alpen ; it, Alpi ; rm, Alps; sl, Alpe ) are the highest ...

, and some other parts of Roman territory. By Roman
inclusive counting Counting is the process of determining the number A number is a mathematical object used to counting, count, measurement, measure, and nominal number, label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be ...
, they were reckoned as "ninth days" although they actually occurred every eighth day. Because the republican and Julian years were not evenly divisible into eight-day periods, Roman calendars included a column giving every day of the year a nundinal letter from A to H marking its place in the cycle of market days. Each year, the letter used for the markets would shift along the cycle. As a day when the city swelled with rural plebeians, they were overseen by the aediles and took on an important role in Roman legislation, which was supposed to be announced for three nundinal weeks (between ) in advance of its coming to a vote. The patricians and their Patronage in ancient Rome, clients sometimes exploited this fact as a kind of filibuster, since the tribunes of the plebs were required to wait another three-week period if their proposals could not receive a vote before dusk on the day they were introduced. Superstitions arose concerning the bad luck that followed a nundinae on the nones of a month or, later, on the January Kalends, first day of January (Roman month), January. Intercalation was supposedly used to avoid such coincidences, even after the Julian reform of the calendar. The 7-day week began to be observed in
Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repubblica Italiana, links=no ), is a country consisting of a peninsula delimited by the Alps The Alps ; german: Alpen ; it, Alpi ; rm, Alps; sl, Alpe ) are the highest ...

in the early imperial period, as practitioners and converts to eastern religions introduced planetary hours, Hellenistic and Babylonian astrology, the Judaism in ancient Rome, Jewish Saturday Jewish sabbath, sabbath, and the Christianity in ancient Rome, Christian Lord's Day. The system was originally used for private worship and astrology but had replaced the nundinal week by the time Constantine I (emperor), Constantine made
Sunday Sunday is the day of the week between Saturday and Monday. In most Western countries, Sunday is a day of rest and a part of the Workweek and weekend, weekend, whereas in much of the rest of the world, it is considered the first day of the week. ...

(') an official day of rest in AD 321. The hebdomadal week was also reckoned as a cycle of letters from A to G; these were adapted for Christian use as the dominical letters.

# Months

The names of Roman months originally functioned as adjectives (e.g., the January kalends occur in the January month) before being treated as substantive nouns in their own right (e.g., the kalends of January occur in January). Some of their etymologies are well-established: January and March honor the gods Janus (god), Janus and Mars (god), Mars; July and August honor
Julius Caesar Gaius Julius Caesar (; 12 July 100 BC – 15 March 44 BC) was a Roman Roman or Romans most often refers to: *, the capital city of Italy *, Roman civilization from 8th century BC to 5th century AD *, the people of ancient Rome *', shortened ...

and his successor, the list of Roman emperors, emperor
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 ...

; and the months Quintilis, Sextilis, September,. October, November, and December are archaic adjectives formed from the ordinal numeral, ordinal numbers from , their position in the calendar when it began around the spring equinox in March. Others are uncertain. February may derive from the Februa festival or its eponymous ' ("purifications, expiatory offerings"), whose name may be either Sabine language, Sabine or preserve an archaic word for sulphuric. April may relate to the Etruscans, Etruscan goddess Apru or the verb ' ("to open"). May and June may honor Maia (goddess), Maia and
Juno Juno commonly refers to: *Juno (mythology), the Roman goddess of marriage and queen of the gods *Juno (film), ''Juno'' (film), 2007 Juno may also refer to: Arts, entertainment and media Fictional characters *Juno, in the film ''Jenny, Juno'' *Jun ...
or derive from archaic terms for "senior" and "junior". A few list of Roman emperors, emperors attempted to add themselves to the calendar after Augustus, but without enduring success. In classical Latin, the days of each month were usually reckoned as:
Dates after the ides count forward to the kalends of the next month and are expressed as such. For example, March19 was expressed as "the 14th day before the April Kalends" ('), without a mention of March itself. The day after a kalends, nones, or ides was also often expressed as the "day after" (') owing to their special status as particularly unlucky "black days". The anomalous status of the new 31-day months under the Julian calendar was an effect of Caesar's desire to avoid affecting the Roman festivals, festivals tied to the nones and ides of various months. However, because the dates at the ends of the month all counted forward to the next kalends, they were all shifted by one or two days by the change. This created confusion with regard to certain anniversaries. For instance,
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 ...

's birthday on the 23rdday of September was ' in the old calendar but ' under the new system. The ambiguity caused honorary festivals to be held on either or both dates.

# Intercalation

The Republican calendar only had 355days, which meant that it would quickly unsynchronize from the solar year, causing, for example, agricultural festivals to occur out of season. The Roman solution to this problem was to periodically lengthen the calendar by adding extra days ''within'' February. February was broken into two parts, each with an odd number of days. The first part ended with the Terminalia on the 23rd ('), which was considered the end of the religious year; the five remaining days beginning with the Regifugium on the 24th (') formed the second part; and the intercalary month
MercedoniusMercedonius (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 Repub ...
was inserted between them. In such years, the days between the ides and the Regifugium were counted down to either the Intercalary Kalends or to the Terminalia. The intercalary month counted down to nones and ides on its 5th and 13th day in the manner of the other short months. The remaining days of the month counted down towards the March Kalends, so that the end of Mercedonius and the second part of February were indistinguishable to the Romans, one ending on ' and the other picking up at ' and bearing the normal festivals of such dates. Apparently because of the confusion of these changes or uncertainty as to whether an intercalary month would be ordered, dates after the February ides are attested as sometimes counting down towards the Quirinalia (Feb.17), the Feralia (Feb.21), or the Terminalia (Feb.23) rather than the intercalary or March kalends. The third-century writer Censorinus says:
When it was thought necessary to add (every two years) an intercalary month of , so that the civil year should correspond to the natural (solar) year, this intercalation was in preference made in February, between the Terminalia [23rd] and Regifugium [24th].
The fifth-century writer Macrobius says that the Romans intercalated in alternate years (''Saturnalia'', 1.13.12); the intercalation was placed after 23February and the remaining five days of February followed (''Saturnalia'', 1.13.15). To avoid the nones falling on a nundine, where necessary an intercalary day was inserted "in the middle of the Terminalia, where they placed the intercalary month". This is historically correct. In 167BC Mercedonius, Intercalaris began on the day after 23February and in 170BC it began on the second day after 23February. Varro, writing in the first centuryBC, says "the twelfth month was February, and when intercalations take place the five last days of this month are removed."Varro, ''On the Latin language'', 6.13, tr. Roland Kent, London 1938, available a

Since all the days after the Ides of Intercalaris were counted down to the beginning of March Intercalaris had either 27days (making 377 for the year) or 28 (making 378 for the year). There is another theory which says that in intercalary years February had and Intercalaris had 27. No date is offered for the Regifugium in 378-day years. Macrobius describes a further refinement whereby, in one 8-year period within a 24-year cycle, there were only three intercalary years, each of 377days. This refinement brings the calendar back in line with the seasons, and averages the length of the year to 365.25days over 24years. The Pontifex Maximus determined when an intercalary month was to be inserted. On average, this happened in alternate years. The system of aligning the year through intercalary months broke down at least twice: the first time was during and after the Second Punic War. It led to the reform of the 191 BC Lex Acilia de Intercalando, Acilian Law on Intercalation, the details of which are unclear, but it appears to have successfully regulated intercalation for over a century. The second breakdown was in the middle of the first century BC and may have been related to the increasingly chaotic and adversarial nature of Roman politics at the time. The position of Pontifex Maximus was not a full-time job; it was held by a member of the Roman elite, who would almost invariably be involved in the machinations of Roman politics. Because the term of office of elected Magistratus ordinarii / extraordinarii, Roman magistrates was defined in terms of a Roman calendar year, a Pontifex Maximus would have reason to lengthen a year in which he or his allies were in power or shorten a year in which his political opponents held office. Although there are many stories to interpret the intercalation, a period of is always synodic month short. Obviously, the month beginning shifts forward (from the new moon, to the third quarter, to the full moon, to the first quarter, back the new moon) after intercalation.

# Years

As mentioned above, Rome's legendary 10-month calendar notionally lasted for 304days but was usually thought to make up the rest of the
solar year A tropical year (also known as a solar year or tropical period) is the time Time is the continued sequence of existence and event (philosophy), events that occurs in an apparently irreversible process, irreversible succession from the past ...
during an unorganized winter period. The unattested but almost certain lunar year and the pre-Julian civil year were long, with the difference from the solar year more or less corrected by an irregular intercalary month. The Julian calendar, Julian year was 365days long, with a
leap day February 29, also known as leap day or leap year day, is a date added to 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 ...
doubled in length every fourth year, almost equivalent to the present Gregorian calendar, Gregorian system. The calendar era before and under the Roman kingdom, Roman kings is uncertain but dating by regnal years was common in antiquity. Under the
Roman Republic The Roman Republic ( la, Rēs pūblica Rōmāna ) was a state of the classical Roman civilization, run through public In public relations Public relations (PR) is the practice of managing and disseminating information from an indiv ...
, from 509BC, years were most commonly described in terms of their reigning Roman consul, ordinary consuls. (Suffect consul, Temporary and honorary consuls were sometimes elected or appointed but were not used in dating.) List of Roman consuls, Consular lists were displayed on the fasti, public calendars. After the institution of 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 ...

, regnal dates based on the emperors' terms in office became more common. Some historians of the later republic and early imperial eras dated from the legendary founding of the city of Rome (' or ). Varro's date for this was 753BC but other writers used different dates, varying by several decades. Such dating was, however, never widespread. After the consuls waned in importance, most Roman dating was regnal. or followed
Diocletian Diocletian (; la, Gaius Aurelius Valerius Diocletianus; born Diocles; 22 December c. 244 – 3 December 311) was from 284 to 305. Born to a family of low status in , Diocletian rose through the ranks of the military to become a commander of ...
's 15-year Indiction tax cycle. These cycles were not distinguished, however, so that "year 2 of the indiction" may refer to any of 298, 313, 328, &c. The Greek Orthodox Church, Orthodox subjects of the
Byzantine Empire The Byzantine Empire, also referred to as the Eastern Roman Empire, or Byzantium, was the continuation of the Roman Empire The Roman Empire ( la, Imperium Rōmānum ; grc-gre, Βασιλεία τῶν Ῥωμαίων, Basileía tôn ...

used various Christian eras, including Anno Martyrum, those based on Diocletian's persecutions, Incarnation (Christianity), Christ's incarnation, and Anno Mundi, the supposed age of the world. The Romans did not have records of their early calendars but, like modern historians, assumed the year originally began in March on the basis of the names of the months following June. The consul Marcus Fulvius Nobilior, M. Fulvius Nobilior (r.189BC) wrote a commentary on the calendar at the Temple of Hercules Musarum that claimed January had been named for Janus (god), Janus because the god faced both ways, suggesting it had been instituted as a first month. It was, however, usually said to have been instituted along with February, whose nature and festivals suggest it had originally been considered the last month of the year. The consuls' term of office—and thus the order of the years under the republic—seems to have changed several times. Their inaugurations were finally moved to 1 January, 1January (') in 153BC to allow Quintus Fulvius Nobilior, Q. Fulvius Nobilior to attack Segeda in Prehistoric Spain, Spain during the Celtiberian Wars, before which they had occurred on 15 March, 15March ('). There is reason to believe the inauguration date had been 1 May, 1May during the until 222BC and
Livy Titus Livius (; 59 BC – AD 17), known in English as Livy ( ), was a Ancient Rome, Roman historian. He wrote a monumental history of Rome and the Roman people, titled , covering the period from the earliest legends of Rome before the traditiona ...
mentions earlier inaugurations on 15May ('), 1July ('), 1August ('), 1October ('), and 15December ('). Under the Julian calendar, the year began on 1January but years of the Indiction cycle began on 1September. In addition to Egyptian calendar, Egypt's separate calendar, some provinces maintained their records using a local era. Africa (Roman province), Africa dated its records sequentially from 39BC; Roman Spain, Spain from AD38. This dating system continued as the Spanish era used in medieval Spain.

# Conversion to Julian or Gregorian dates

The continuity of names from the Roman to the
Gregorian calendar The Gregorian calendar is 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, speci ...
can lead to the mistaken belief that Roman dates correspond to Julian or Gregorian ones. In fact, the essentially complete
list of Roman consuls This is a list of Roman consul, consuls known to have held office, from the beginning of the Roman Republic to the latest use of the title in Roman Empire, Imperial times, together with those magistrates of the Republic who were appointed in plac ...
allows general certainty of years back to expulsion of Tarquin, the establishment of the
republic A republic () is a form of government A government is the system or group of people governing an organized community, generally a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a month ...
but the uncertainty as to the end of lunar dating and the irregularity of Roman intercalation means that dates which can be independently verified are invariably weeks to months outside of their "proper" place. Two astronomical events dated by
Livy Titus Livius (; 59 BC – AD 17), known in English as Livy ( ), was a Ancient Rome, Roman historian. He wrote a monumental history of Rome and the Roman people, titled , covering the period from the earliest legends of Rome before the traditiona ...
show the calendar 4 months out of alignment with the Julian date in 190BC and 2 months out of alignment in 168BC. Thus, "the year of the consulship of Publius Cornelius Scipio Africanus and Publius Licinius Crassus Dives (consul 205 BC), Publius Licinius Crassus" (usually given as "205BC") actually began on 15March 205BC and ended on 14March 204BC according to the Roman calendar but may have begun as early as November or December 206BC owing to its misalignment. Even following the establishment of the
Julian calendar 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 B ...
, the leap years were not applied correctly by the Roman priests, meaning dates are a few days out of their "proper" place until a few decades into Augustus's reign. Given the paucity of records regarding the state of the calendar and its intercalation, historians have reconstructed the correspondence of Roman dates to their Julian and Gregorian equivalents from disparate sources. There are detailed accounts of the decades leading up to the Julian reform, particularly the speeches and letters of Cicero, which permit an established chronology back to about 58BC. 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 ...
and a few known synchronisms—e.g., a Roman date in terms of the Attic calendar and Olympiad—are used to generate contested chronologies back to the start of the First Punic War in 264BC. Beyond that, dates are roughly known based on clues such as the dates of harvests and seasonal religious festivals.

* List of calendars * Julian calendar, Julian, Alexandrian calendar, Alexandrian, Byzantine calendar, Byzantine, &
Gregorian calendar The Gregorian calendar is 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, speci ...
s * List of Roman consuls and ''ab urbe condita'' dating * General Roman Calendar of the Catholic Church * Roman festivals * Undecimber

# References

## Bibliography

* . * . * . * * . * . * . * . * . & * . * . * . * . * . * . * . * . * . * . * . * . * . * . * .