The Byzantine Empire, also known as the Eastern Roman Empire, was the continuation of the Roman Empire centred on Constantinople during late antiquity and the Middle Ages. Having survived the events that caused the fall of the Western Roman Empire in the 5th century AD, it endured until the fall of Constantinople to the Ottoman Empire in 1453. The term 'Byzantine Empire' was coined only after its demise; its citizens used the term 'Roman Empire' and called themselves 'Romans'.[a]

During the early centuries of the Roman Empire, the western provinces were Latinised, but the eastern parts kept their Hellenistic culture. Constantine I (r. 324–337) legalised Christianity and moved the capital to Constantinople. Theodosius I (r. 379–395) made Christianity the state religion and Greek gradually replaced Latin for official use. The empire adopted a defensive strategy and, throughout its remaining history, experienced recurring cycles of decline and recovery.

The Byzantine Empire reached its greatest extent under the reign of Justinian I (r. 527–565), who briefly reconquered much of Italy and the western Mediterranean coast. A plague began around 541, and a prolonged warfare with Persia placed fiscal and military strain on the empire, contributing to political and strategic challenges in the decades that followed. In the 630s and 640s the Arab conquests defeated Byzantine field armies in Syria and Egypt, resulting in the permanent loss of those provinces to the Rashidun Caliphate. In 698, Africa was lost to the Umayyad Caliphate, but the empire stabilised under the Isaurian dynasty. It expanded once more under the Macedonian dynasty, experiencing a two-century-long renaissance. Thereafter, periods of civil war and Seljuk incursion resulted in the loss of most of Asia Minor. The empire recovered during the Komnenian restoration, and Constantinople remained the largest and wealthiest city in Europe until the 13th century, when it was overtaken by Paris.

The empire was severely fragmented in 1204, following the sack of Constantinople during the Fourth Crusade; its former territories were then divided into competing Greek rump states and Latin realms. Despite the eventual recovery of Constantinople in 1261, the reconstituted empire wielded only regional power during its final two centuries. Its remaining territories were progressively annexed by the Ottomans in a series of wars fought in the 14th and 15th centuries. The fall of Constantinople to the Ottomans in 1453 brought the empire to an end.

NomenclatureSee also: Names of the GreeksThe empire's inhabitants, today generally known as Byzantines, regarded themselves as Romans (in Greek, Ῥωμαῖοι or Romaioi).[6] Similarly, their Islamic contemporaries called their empire the land of the Romans (Bilād al-Rūm).[7] After 800 AD, Western Europe called them Greeks (Graeci), as the Papacy and medieval German emperors regarded themselves as the true inheritors of Roman identity.[8] The adjective Byzantine, derived from Byzantion (Byzantium in Latin), the name of the Greek settlement Constantinople was established on, was only used to describe the inhabitants of the city; it did not refer to the empire, called Rhomanía (Ῥωμανία or Romanland) by its citizens.[9]

Following the empire's fall, early modern scholars referred to it by many names, including the Eastern Empire, the Low Empire, the Late Empire, the Empire of the Greeks, Empire of Constantinople, and Roman Empire.[10] The increasing use of Byzantine and Byzantine Empire may have started with Theodore Metochites[11] or Laonikos Chalkokondyles whose work was widely propagated by Hieronymus Wolf.[12] Byzantine was used adjectivally alongside terms such as Empire of the Greeks until the 19th century.[13] It is now the primary term, used to refer to all aspects of the empire; a minority of modern historians believe it should not be used because it was originally a prejudicial and inaccurate term.[14]