Christianity in Turkey
Constantinople became established in the ecclesiastical hierarchy at the Council of Constantinople in 381. Second only to Rome, the legendary origins of the Patriarchate of Constantinople go back to St. Andrew, Metrophanes and Alexander of Constantinople. Constantinople's primacy over the Patriarchates of Alexandria and Antioch was reaffirmed at the Council of Chalcedon in 481, after which the papacy in Rome supported Constantinople in its dispute with Alexandria over monophysitism. Later, when Rome sought to assert its primacy over Byzantium, the Eastern Orthodox church developed the doctrine of pentarchy as a response.
Western Roman Empire
Constantius II focused most of his power in the East. Under his rule, the city of Byzantium – only recently re-founded as Constantinople – was fully developed as a capital. At Constantinople, the political, economic and military control of the Eastern Empire's resources would remain safe for centuries to come. The city was well fortified and located at the crossroads of several major trade and military routes. The site had been acknowledged for its strategic importance already by emperors Septimius Severus and Caracalla, more than a century prior.