The Arabs knew the Byzantine Empire simply as Rum. Byzantine and Persia were two-world super-powers just before the rise of Islam. The Emperor Constantine founded its capital Constantinople, in 330 A.D, but was separated from the West only at the death of Theodosius in 395. Thereafter the East developed and prospered, while the West became prey to the invasion of the vandals, who even sacked Rome, and ushered in the “dark ages” of Europe.
The national basis of Byzantine was Greece, but the empire spread over parts of Eastern Europe, all of modern Turkey (not yet inhabited by Turks), Syria, Palestine, Iraq, Egypt and the north coast of Africa. The language of the empire was Greek, which had taken root in most of the Middle East from the time of Alexander’s empire in 333B.C. Greek remained the market language during the period of Latin Roman domination (in the time of Christ), and was the sole imperial language after the Byzantine separation from the West. The predominant religion since the time of Constantine was Orthodox Christianity. The East always had its own liturgical practices, different from the West, but was united with Rome until the Schism of 1009. The areas were parts of the Byzantine Empire neighbouring Arabia, and were involved in the rise of Islam, Egypt, Syria, Palestine, Iraq and Persian Empire.