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 the East–West Schism
After the sole emperor of all the Roman Empire Constantine built the new imperial capital at Byzantium, a strategically placed city on the Bosporus. He renamed his new capital "Nova Roma" ("New Rome"), but the city would become known as Constantinople. The centre of gravity in the empire was fully recognised to have completely shifted to the eastern Mediterranean. Rome lost the Senate to Constantinople and lost its status and gravitas as imperial capital, see also Fall of Rome.
Soon the local bishop was elevated to Patriarch under Constantine, as Metrophanes of Byzantium
The patriarchs of Constantinople often tried to adopt an imperious position over the other patriarchs. In the case of Nestorius, whose actual teaching is now recognised to be not overtly heretical, although it is clearly deficient, (Saint Cyril called it 'slippery'), other patriarchs were able to make the charge of heresy stick and successfully had him deposed. This was probably more because his Christology was delivered with a heavy sarcastic arrogance which matched his high-handed personality.
In the fourth century, when the Roman emperors (reigning in Constantinople) were trying to control the Church, theological questions ran rampant throughout the Roman Empire. The influence of Greek speculative thought on Christian thinking led to all sorts of divergent and conflicting opinions. Theology was also used as a weapon against opponent bishops, because being branded a heretic was the only sure way for a bishop to be removed by other bishops—incompetence was not sufficient grounds for removal.