The eastern half of the Roman empire. Emperor Constantine (306–34) had reunited the two halves, divided by Diocletian (284–305), and had refounded the Greek city of Byzantium as his eastern capital, calling it Constantinople (now Istanbul) (330). At his death in 395 Emperor Theodosius divided the empire between his sons. After the fall of Rome to the Ostrogoths (476) Constantinople was the capital of the empire and was famous for its art, architecture, and wealth. While barbarian invaders overran the Western empire, the Byzantine emperors always hoped to defeat them and reunite the empire. Emperor Justinian reconquered North Africa and part of Italy, making Ravenna the western capital, but his success was shortlived.

After Muhammad’s death (632) Muslim Arab forces swept through Persia and the Middle East, across North Africa, and into Spain. By 750 only the Balkans and Asia Minor remained unconquered. From the 9th century Charlemagne’s Frankish empire dominated the West. In the 8th and 9th centuries religious disunity, notably the Iconoclastic controversy, weakened the empire. Theological and political differences between Rome and Constantinople led to the East–West Schism between Latin and Orthodox Christianity. (1054). The vigorous emperor Alexius Comnenus (1081–1118) defeated barbarian attacks from the north and appealed to the Franks for help against the Seljuk Turks. In the 12th century, some reconquests were made in Asia Minor and the period was one of achievement in literature and art, only brought to an end by the Frankish sack of Constantinople in 1204. The failure to achieve any united Christian opposition to the Turks and the growing independence of the Balkan princedoms weakened the empire. Ottoman incursions in the 14th and 15th centuries culminated in the capture of Constantinople in 1453 and the end of the empire.