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.
History of Europe
In the 4th century, the emperors Diocletian and Constantine were able to slow down the process of decline by splitting the empire into a Western part with a capital in Rome and an Eastern part with the capital in Byzantium, or Constantinople (now Istanbul). Whereas Diocletian severely persecuted Christianity, Constantine declared an official end to state-sponsored persecution of Christians in 313 with the Edict of Milan, thus setting the stage for the Church to become the state church of the Roman Empire in about 380.