The change of territory of the Byzantine Empire (476–1400)
and largest city
Roman Empire in its eastern provinces during Late Antiquity and the Middle Ages, when its capital city was Constantinople (modern Istanbul, formerly Byzantium). It survived the fragmentation and fall of the Western Roman Empire in the 5th century AD and continued to exist for an additional thousand years until it fell to the Ottoman Empire in 1453. During most of its existence, the empire was the most powerful economic, cultural, and military force in Europe. "Byzantine Empire" is a term created after the end of the realm; its citizens continued to refer to their empire simply as the Roman Empire (Greek: Βασιλεία Ῥωμαίων, tr. Basileía Rhōmaíōn; Latin: Imperium Romanum), or Romania (Greek: Ῥωμανία, romanized: Rhōmanía), and to themselves as Romans (Greek: Ῥωμαῖοι, romanized: Rhōmaîoi). Several signal events from the 4th to 6th centuries mark the period of transition during which the Roman Empire's Greek East and Latin West diverged. Constantine I (r. 324–337) reorganised the empire, made Constantinople the new capital and legalised Christianity. Under Theodosius I (r. 379–395), Christianity became the state religion and other religious practices were proscribed. In the reign of Heraclius (r. 610–641), the Empire's military and administration were restructured and adopted Greek for official use in place of Latin.
Although the Roman state continued and its traditions were maintained, modern historians distinguish Byzantium from ancient Rome insofar as it was centred on Constantinople, oriented towards Greek rather than Latin culture and characterised by Eastern Orthodox Christianity.
The borders of the empire fluctuated through cycles of decline and recovery. During the reign of Justinian I (r. 527–565), the empire reached its greatest extent, after reconquering much of the historically Roman western Mediterranean coast, including North Africa, Italy and Rome, which it held for two more centuries. The Byzantine–Sasanian War of 602–628 exhausted the empire's resources, and during the Early Muslim conquests of the 7th century, it lost its richest provinces, Egypt and Syria, to the Rashidun Caliphate. During the Macedonian dynasty (10th–11th centuries), the empire expanded again and experienced the two-century long Macedonian Renaissance, which came to an end with the loss of much of Asia Minor to the Seljuk Turks after the Battle of Manzikert in 1071. This battle opened the way for the Turks to settle in Anatolia.
The empire recovered during the Komnenian restoration, and by the 12th century Constantinople was the largest and wealthiest city in Europe. The Byzantine Empire was delivered a mortal blow during the Fourth Crusade, when Constantinople was sacked in 1204 and the territories that the empire formerly governed were divided into competing Byzantine Greek and Latin realms. Despite the eventual recovery of Constantinople in 1261, the Byzantine Empire remained only one of several small rival states in the area for the final two centuries of its existence. Its remaining territories were progressively annexed by the Ottomans in the Byzantine–Ottoman wars over the 14th and 15th centuries. The fall of Constantinople to the Ottoman Empire in 1453 ended the Byzantine Empire. The last of the imperial Byzantine successor states, the Empire of Trebizond, would be conquered by the Ottomans eight years later in the 1461 siege.
The first use of the term "Byzantine" to label the later years of the Roman Empire was in 1557, 104 years after the empire's collapse, when the German historian Hieronymus Wolf published his work Corpus Historiæ Byzantinæ, a collection of historical sources. The term comes from "Byzantium", the name of the city to which Constantine moved his capital, leaving Rome, and rebuilt under the new name of Constantinople. The older name of the city would rarely be used from this point onward except in historical or poetic contexts. The publication in 1648 of the Byzantine du Louvre (Corpus Scriptorum Historiae Byzantinae), and in 1680 of Du Cange's Historia Byzantina further popularised the use of "Byzantine" among French authors, such as Montesquieu. However, it was not until the mid-19th century that the term came into general use in the Western world.
The Byzantine Empire was known to its inhabitants as the "Roman Empire", the "Empire of the Romans" (Latin: Imperium Romanum, Imperium Romanorum; Greek: Βασιλεία τῶν Ῥωμαίων Basileia tōn Rhōmaiōn, Ἀρχὴ τῶν Ῥωμαίων Archē tōn Rhōmaiōn), Romania (Latin: Romania; Greek: Ῥωμανία Rhōmania),[note 1] the Roman Republic (Latin: Res Publica Romana; Greek: Πολιτεία τῶν Ῥωμαίων Politeia tōn Rhōmaiōn), and also as "Rhōmais" (Greek: Ῥωμαΐς). The inhabitants called themselves Romaioi and even as late as the 19th century Greeks typically referred to Modern Greek as Romaiika "Romaic". After 1204 when the Byzantine Empire was mostly confined to its purely Greek provinces the term 'Hellenes' was increasingly used instead.
While the Byzantine Empire had a multi-ethnic character during most of its history and preserved Romano-Hellenistic traditions, it became identified by its western and northern contemporaries with its increasingly predominant Greek element. Western medieval sources also referred to the empire as the "Empire of the Greeks" (Latin: Imperium Graecorum) and to its emperor as Imperator Graecorum (Emperor of the Greeks); these terms were used to distinguish it from the Holy Roman Empire that claimed the prestige of the classical Roman Empire in the West.
No such distinction existed in the Islamic and Slavic worlds, where the Empire was more straightforwardly seen as the continuation of the Roman Empire. In the Islamic world, the Roman Empire was known primarily as Rûm. The name millet-i Rûm, or "Roman nation," was used by the Ottomans until the 20th century to refer to the former subjects of the Byzantine Empire, that is, the Orthodox Christian community within Ottoman realms.
The Roman army succeeded in conquering many territories covering the Mediterranean region and coastal regions in southwestern Europe and North Africa. These territories were home to many different cultural groups, both urban populations, and rural populations. Generally speaking, the eastern Mediterranean provinces were more urbanized than the western, having previously been united under the Macedonian Empire and Hellenised by the influence of Greek culture.
The West also suffered more heavily from the instability of the 3rd century AD. This distinction between the established Hellenised East and the younger Latinised West persisted and became increasingly important in later centuries, leading to a gradual estrangement of the two worlds.
An early instance of the partition of the Empire into East and West occurred in 293 when Emperor Diocletian created a new administrative system (the tetrarchy), to guarantee security in all endangered regions of his Empire. He associated himself with a co-emperor (Augustus), and each co-emperor then adopted a young colleague given the title of Caesar, to share in their rule and eventually to succeed the senior partner. Each tetrarch was in charge of a part of the Empire. The tetrarchy collapsed, however, in 313 and a few years later Constantine I reunited the two administrative divisions of the Empire as sole Augustus.
Christianization and partition of the Empire