The city has been the seat of the Ecumenical Patriarchate of Constantinople since the 4th century AD. The city is also seat of the Autocephalous Turkish Orthodox Patriarchate and the Armenian Patriarchate. The city was formerly also the seat of the reduced Bulgarian Orthodox Exarchate, before its autocephaly was recognised for a second time by other bodies of the Orthodox Church.
The everyday life of the Christians, particularly the Greeks and Armenians living in Istanbul changed significantly following the bitter conflicts between these ethnic groups and the Turks during the fall of the Ottoman Empire, which began in the 1820s and continued for a century. The conflicts reached their culmination in the decade between 1912 and 1922; during the Balkan Wars, the First World War and the Turkish War of Independence. The Christian population declined from 450,000 to 240,000 between 1914 and 1927.[99] Today, most of Turkey's remaining Greek and Armenian minorities live in or near Istanbul. The number of the local Turkish Armenians in Istanbul today amount to approximately 45,000[100] (not including the nearly 40,000 Armenian workers in Turkey who came from Armenia after 1991 and mostly live and work in Istanbul);[101] while the Greek community, which amounted to 150,000 citizens in 1924,[102] currently amounts to approximately 4,000 citizens.[100] There are also 60,000 Istanbulite Greeks who currently live in Greece but continue to retain their Turkish citizenship.[100]
The Sephardic Jews have lived in the city for over 500 years. They fled the Iberian Peninsula during the Spanish Inquisition of 1492, when they were forced to convert to Christianity after the fall of the Moorish Kingdom of Andalucia.