The capital, once Byzantium, chosen by the Roman emperor Constantine I (reigned 306-337 AD). He built the Great Palace which has since been enlarged and altered. Constantinople was the principal residence of Byzantine emperors until about end of 11th c AD. Constantine's choice of capital had profound effects upon the ancient Greek and Roman worlds. It displaced the power center of the Roman Empire, moving it eastward, and achieved the first lasting unification of Greece. (İstanbul, Istanbul)