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.
Fall of Constantinople
Byzantium is a term used by modern historians to refer to the later Roman Empire. In its own time, the Empire ruled from Constantinople (or "New Rome" as some people call it, although this was a laudatory expression that was never an official title) was considered simply as "the Roman Empire." The fall of Constantinople led competing factions to lay claim to being the inheritors of the Imperial mantle. Russian claims to Byzantine heritage clashed with those of the Ottoman Empire's own claim. In Mehmed's view, he was the successor to the Roman Emperor, declaring himself "Kayser-i Rum", literally "Caesar of Rome", that is, of the Roman Empire, though he was remembered as "the Conqueror". He founded a political system that survived until 1922 with the establishment of the Republic of Turkey.