The Byzantine Empire was a continuation of the Roman Empire—its citizens even called themselves Romans. Two dates are given for the formation of the Byzantine Empire, which, though boundaries shifted constantly, was centered in Asia Minor and the Balkan Peninsula: In A.D. 395, upon the death of emperor Theodosius the Great, the Roman Empire was divided into two: East and West. In the years that followed, the West Roman Empire was subject to repeated attacks from nomadic barbarian groups, and Rome finally fell in 476. The East Roman Empire survived as the Byzantine Empire, which, after the fall of Rome, laid claim to much of the lands in the west.

However, many historians date the beginning of the Byzantine Empire earlier—at A.D. 330, when Roman emperor Constantine the Great moved the capital of the then united Roman Empire from Rome to Byzantium (present-day Istanbul, Turkey—sub-sequently known as Constantinople). By this definition of the empire, Constantine the Great was its first ruler. He was succeeded by nearly 100 rulers over the course of more than 1,000 years of Byzantine rule. At its height, during the sixth century reign of Justinian I from 483 to 565, the empire included parts of southern and eastern Europe, northern Africa, and the Middle East. The Byzantine Empire ended when the Ottoman Turks conquered Constantinople in 1453.