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.
East–West Schism
The bishop of Byzantium was under the authority of the metropolitan of Heraclea when in 330 Roman Emperor Constantine I moved his residence to this town, which, rebuilt on a larger scale, became known as Constantinople. Thereafter, the bishop's connection with the imperial court meant that he was able to free himself from ecclesiastical dependency on Heraclea and in little more than half a century to obtain recognition of next-after-Rome ranking from the First Council of Constantinople (381), held in the new capital. No Western bishop took part in this council, and the Latin Church recognized it as ecumenical only in the mid-6th century. It decreed: "The Bishop of Constantinople, however, shall have the prerogative of honour after the Bishop of Rome; because Constantinople is New Rome", thus raising it above the sees of Alexandria and Antioch. This has been described as sowing the seed for the ecclesiastical rivalry between Constantinople and Rome that was a factor leading to the schism between East and West. The website of the Orthodox Church in America says that the Bishop of Byzantium was elevated to Patriarch already in the time of Constantine.