|Eastern division of the Roman Empire|
- Latin (official until 610)
- Greek (official after 610)
|Religion||Christianity (Eastern Orthodox)|
(tolerated after the Edict of Milan in 313; state religion after 380)
| • ||285–305||Diocletian|
| • ||324–337||Constantine I|
| • ||457–474||Leo I|
| • ||527–565||Justinian I|
| • ||610–641||Heraclius|
| • ||717–741||Leo III|
| • ||976–1025||Basil II|
| • ||1081–1118||Alexios I|
| • ||1449–1453||Constantine XI|
|Historical era||Late Antiquity to Late Middle Ages|
| • ||Partition of the Roman Empire||285|
| • ||Founding of Constantinople||330|
| • ||Death of Theodosius I||395|
| • ||Nominal end of the Western Roman Empire||476|
| • ||Fourth Crusade; establishment of Latin Empire||1204|
| • ||Reconquest of Constantinople by Palaiologos||1261|
| • ||Fall of Constantinople||29 May 1453c|
| • ||Fall of Trebizond||15 August 1461|
| • ||565 AD est.||26,000,000d |
| • ||780 AD est.||7,000,000 |
| • ||1025 AD est.||12,000,000 |
|Currency||Solidus, hyperpyron and follis|
|a.||^ Βασιλεία Ῥωμαίων may be transliterated in Latin as Basileia Rhōmaiōn, meaning Roman Empire.|
|b.||^ Theodosius I was the last emperor to rule over both the Eastern and Western Roman Empire. He died in 395 AD after making Christianity the official religion of the empire.|
|c.||^ Between 1204 and 1261 there was an interregnum when the Empire was divided into the Empire of Nicaea, the Empire of Trebizond and the Despotate of Epirus, which were all contenders for rule of the Empire. The Empire of Nicaea is considered the legitimate continuation of the Byzantine Empire because they managed to re-take Constantinople.|
|d.||^ See Population of the Byzantine Empire for more detailed figures taken provided by McEvedy and Jones, Atlas of World Population History, 1978, as well as Angeliki E. Laiou, The Economic History of Byzantium, 2002.|
The Byzantine Empire, also referred to as the Eastern Roman Empire, was the continuation of the Roman Empire in the East during Late Antiquity and the Middle Ages, when its capital city was Constantinople (modern-day Istanbul, which had been founded as 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 Turks in 1453. During most of its existence, the empire was the most powerful economic, cultural, and military force in Europe. Both "Byzantine Empire" and "Eastern Roman Empire" are historiographical terms created after the end of the realm; its citizens continued to refer to their empire as the Roman Empire (Greek: Βασιλεία τῶν Ῥωμαίων, tr. Basileia tôn Rhōmaiōn; Latin: Imperium Romanum), or Romania (Ῥωμανία), and to themselves as "Romans."
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 divided. 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 Empire's official state religion and other religious practices were proscribed. Finally, under the reign of Heraclius (r. 610–641), the Empire's military and administration were restructured and adopted Greek for official use instead of Latin. Thus, although the Roman state continued and Roman state 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 Orthodox Christianity.
The borders of the Empire evolved significantly over its existence, as it went through several 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 itself, which it held for two more centuries. During the reign of Maurice (r. 582–602), the Empire's eastern frontier was expanded and the north stabilised. However, his assassination caused the Byzantine–Sasanian War of 602–628, which exhausted the Empire's resources and contributed to major territorial losses during the Early Muslim conquests of the seventh century. In a matter of years the Empire lost its richest provinces, Egypt and Syria, to the Arabs.
During the Macedonian dynasty (10th–11th centuries), the Empire again expanded 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 again during the Komnenian restoration, such that by the 12th century Constantinople was the largest and wealthiest European city. However, it 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 over the 14th and 15th century. The Fall of Constantinople to the Ottoman Empire in 1453 finally 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 of Trebizond.