Istanbul met Christianity in the 4th century, while, Paganism was dominant before.
The first Christian churches are Havariyyun, Haghia Sophia and Haghia Eirene. Many churches had been built until the conquest of Istanbul. There the churches of different sects and religious orders such as Nestorianism, Monophysism, Catholicism, Orthodoxy, Syrian Christianity, Gregorianism, Keldani, Dominicanism, Franciscanism has been in Istanbul. Moreover, different nations such as Greek, Armenian, Latin and Genoese also has had their own churches.
The Armenian Patriarchate
The Armenian Patriarchate in Istanbul is one of the four hierarchical centers of the Armenian Church -the others are in Erivan, Beirut and Jerusalem. The first patriarch of Istanbul, Hovaghim I, was in charge during the reign of Fatih Sultan Mehmet. Since r64i, the Virgin Mary (Meryem Ana) Central Church and the traditional wooden Patriarchate building of Istanbul Armenian Patriarchate is in Kumkap