Theocatic republic and former monarchy of southwestern Asia. It is thought that Christianity was preached in this region in the 1st century. The spread of the Faith, mainly through missionaries from Syria, was usually encouraged or tolerated until the 3rd century when the Sassanian dynasty revived Zoroastrianism as the state religion of their large empire. When Christianity was adopted by Constantine and invoked on behalf of the Roman Empire, in 312, the many thousands of Christians within the rival Persian Empire who were still under the ecclesiastical authority of Antioch were regarded with increasing suspicion of political disloyalty. They were severely persecuted, but their numbers continued to grow. The writings of Aphraates, a Christian Persian noble, remain as important evidence of the beliefs of this period. Schools and libraries at Nisibis (modern Nisibin) and Edessa (Urfa) were founded by Saint James, Bishop of Nisibis, and his pupil, Saint Ephraem, and were famous centers of Syriac culture. In the 5th century many Nestorian Christians immigrated to Persia. The whole Church in Persia became Nestorian, and it continued to flourish as such for a few centuries after the Arab conquest and the adoption of Islam by the majority of Persians. There were many monasteries, and Nestorian missionaries were sent to India, China, and Mongolia. In the 17th century colonies of Armenians and Georgians settled in Persia, and at various times since then there have been other immigrations of Christians. Those successors of the ancient Nestorians who have come into union with Rome form the Chaldean Church. In 1935 the name of the land was changed to Iran. In 1979 the ruling monarch was overthrown and conservative Islamic clerics took power. There are perhaps 10,000 Roman Catholics in the country.
Ecclesiastically the country is governed by