The Ecumenical Patriarchate of Constantinople (65-present) is an autocephalous church of Orthodox Christianity, headquartered at the Church of St. George in Istanbul, Turkey. It was founded by Saint Andrew in 65 AD during the reign of the Roman Empire over what was then the city of Byzantium, which was later renamed to Constantinople and became a city of the Byzantine Empire. The patriarchate has existed for almost 2,000 years despite Islam being the dominant religion in the country since 1453 and the Ottoman Empire at times persecuting non-Muslims. Although the Orthodox Church does not have a nominal head such as a pope, the Ecumenical Patriarch is considered to be the leader of the world's 300,000,000 Orthodox Christians.