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.
Constantinople
Constantine's foundation gave prestige to the Bishop of Constantinople, who eventually came to be known as the Ecumenical Patriarch, and made it a prime center of Christianity alongside Rome. This contributed to cultural and theological differences between Eastern and Western Christianity eventually leading to the Great Schism that divided Western Catholicism from Eastern Orthodoxy from 1054 onwards. Constantinople is also of great religious importance to Islam, as the conquest of Constantinople is one of the signs of the End time in Islam.The city provided a defence for the eastern provinces of the old Roman Empire against the barbarian invasions of the 5th century. The 18-meter-tall walls built by Theodosius II were, in essence, impregnable to the barbarians coming from south of the Danube river, who found easier targets to the west rather than the richer provinces to the east in Asia. From the 5th century, the city was also protected by the Anastasian Wall, a 60-kilometer chain of walls across the Thracian peninsula. Many scholars argue that these sophisticated fortifications allowed the east to develop relatively unmolested while Ancient Rome and the west collapsed.