The Church of the East (most of whose members are ethnic Assyrians) traced its origins to the evangelism of Saint Paul and Saint Thomas. The Church traces its roots after the apostles to the See of Babylon, said to have been founded by Saint Thomas. In the 5th century the Church of the East offered protection to followers of the Nestorian movement, declared heretical in the Roman Empire at the First Council of Ephesus. As such it accepted only the first two Ecumenical Councils — the Council of Nicaea and the First Council of Constantinople — as defining its faith tradition. Despite severe persecutions, the Church of the East prospered under the Parthian and SasanianEEmpires and, following the Muslim conquest of Persia, the Islamic Caliphate. During the era of the Islamic Empire, the Church of the East was made a protected dhimmi community and largely maintained their autonomy; in a fatwa, the Islamic Prophet Muhammad demanded the protection of the Assyrian people of Mesopotamia.