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.
Battle of Chrysopolis
A year later, Constantine's nephew the younger Licinius also fell victim to the emperor's anger or suspicions. In defeating his last foe, Licinius, Constantine became the sole emperor of the Roman empire; the first such since the elevation of Maximian to the status of augustus by Diocletian in April 286. After his conquest of the eastern portion of the Roman Empire Constantine made the momentous decision to give the east its own capital, and the empire as a whole its second. He chose the city of Byzantium — renamed "Constantinopolis" — as the site of this new foundation.Primary sources