We begin with the Nestorians as they constitute the oldest of the existing dissident Churches. The Arians, Novatians, Paulinists, and scores of other heretics who gave such trouble to the early Christian Church have long disappeared and only students of heresiology now know what doctrines they really professed. The distinguishing tenet of Nestorianism, which owes its origin to Nestorius, Patriarch of Constantinople from 428 to 431, is the assertion that in Christ there are two persons--the human and the divine--and the denial that the Mother of Christ is the Mother of God. The Catholic doctrine, as defined by the third Œcumenical Council held at Ephesus in 431, is that in Christ there is but one person--the person of the Son of God--and that the Blessed Virgin Mary is the Mother of God--Θεοτόκος. From its beginning Nestorianism has been essentially an eastern organization and was early adopted by the successors of the “Parthians, Medes, Elamites, and inhabitants of Mesopotamia,” who, on the first Pentecost, were so amazed to hear the Apostles in Jerusalem speaking in divers tongues the wonderful works of God.[321] On account of political and other reasons, the Nestorians soon became separated from the rest of Christendom. Banished from Edessa in 489 by the Emperor Zeno, they fled to Nisibis which then belonged to Persia. The Persian King, learning that they did not profess the same creed as that held by the Byzantines, with whom he was always at war, took them under his protection. From that time the Nestorian Church, which eventually became almost forgotten west of Mesopotamia, had an extraordinary development in the East. For, although from his palace, in the twin city of Seleucia-Ctesiphon, the Nestorian Katholicos sent missionaries to Arabia and Syria and Egypt, by far the larger number went to far-off India and China. In the thirteenth and fourteenth centuries, when the Nestorian Church attained its greatest development, the jurisdiction of the Nestorian Katholicos rivaled in extent that of the greatest of the Byzantine Patriarchs. For then the supreme head of the Nestorians ruled over a vast number of bishops who were stationed at important points in Asia from Mosul to Malabar and from Jerusalem to Java and Peking.[322]