The Early Byzantine period
  The Byzantine Empire is in fact the Late Roman Empire, centered on Constantinople, the New Rome. The term derives from Byzantium, the ancient Greek colony chosen by Constantine I (307-337) to become his new imperial capital and renamed Constantinople. The citizens of Constantinople were commonly refered to as Byzantines, but they identified themselves, like the rest of the empire's inhabitants, as Romans or simply as Christians. The foundation of Constantinople in 324 and the conquest o0f the same city by the Ottoman Turks in 1453 arbitrarily but conveniently mark the rise and fall of the Byzantine Empire. During these eleven centuries, Roman administrative tradition, Christian religion, and Greek language formed the character of the empire, while massive territorial loss profoundly altered its physical aspect.
  Byzantine history can be divided into three periods, the Early, the Middle and the Late. The Early Byzantine period may be regarded as extending to about the middle of the seventh century, which saw the rise of Islam and the definite installation of the Arabs along the eastern and southern shores of the Mediterranean; the Middle period, to the occupation of Asia Minor by the Turks in the 1070s or to the capture of Constantinople by the Crusaders in 1204; the Late period, from either one of these dates to 1453.
  The Early Byzantine empire (fourth to seventh centuries) had largely the territory and administrative structures of its Roman progenitor. However, the foundation of Constantinople on the Bosphorus strait (modern Turkey), initiated an eastward shift which facilitated the secession of western provinces. By the sixth century, most of the western territories had been invaded by barbarians. Rome itself was sacked twice (410 and 455), and was replaced by Ravenna as the capital of the Ostrogothic kingdom. The tolerance of Christianity by decree in 313, and its subsequent endorsement by most Roman emperors, was of equal significance. Christianity spread around the Meditteranean gaining in complexity and wealth, gradually displacing pagan religion. The materials and vocabulary of late Roman art and architecture were adapted to Christian purposes. The fourth and fifth centuries saw the emergeance of new forms, the maturity of which produced, in the sixth century, a Byzantine art and architecture that acknowledged but were largely independent of their Roman origins.