Name given to Christians who adhered to the heresy attributed to Nestorius, (ca 451) Archbishop of Constantinople, (429-431) native of Germanicia in SyriaEuphratensis as a to members of the Persian Church, called variantly “The Church of the East", the "East Syrian Church", the "Chaldean Syrian Church", the 'Nestorian Church" etc., Today the remnants of this once great church are to be seen mainly in Iraq, India and the U. S. A.
Traditional headquarters of the Nestorian Church was Seleucia, 60 miles from Baghdad, now known as Salman Pak. Origins are obscure: traditionally the founding of the Church is attributed to Mar Mari, presumed to be one of the 70 disciples of Christ, or at least a disciple of St. Thomas the Apostle. Origen (See Eusebius, H.E. I:IlI:C.l:l) attributes the evangelisation of Parthia to St.Thomas himself; others would claim the Apostle Thaddeus (Mar Adai) as the founder;
Refugees feeing persecution in the Roman empire under Emperors Decius (249 AD) and Diocletian (303-304 AD) replenished the rank of the Persian Christians. Mar Baba (Papa), Metropolitan of Seleucia at the end of the 3rd century, organized the Persian Church. The theological school of Nisibis, later transferred to Edessa (363 AD) was the spiritual centre of the Church; St.Ephrem Syrus (Ca 306-373) taught at both Edessa and Nisibis.
Nestorius did not belong to the Persian Church, nor did he obviously know Syriac or Persian. The Persian Church was not party to the Nestorian Controversy, culminating in the condemnation of Nestorius in 431 at Ephesus. The Persian Church had already severed connections with the Byzantine Church, mainly for political reasons, and declared itself an autonomous church, at the Synod of Markabta, presided over by Dadisho, in 424; and hence took no part in the Nestorian-Eutychian and Chalcedonian controversies within the Byzantine empire.
The Persian Church was itself severely persecuted by the Persian Government, under Sapor II (339—379 AD) Bahram V (Ca 420 AD) and Yezdegerd I1 (Ca 448 AD). But it developed strong monastic, theological and missionary movements during this period; the faith spread not only in Persia, but also in Arabia -- specifically in Hirtha Kufa, Najran, Yemen, Zafar, Aden, Sana, Hrmuz.
The most impressive missionary expansion of ancient history began under Patriarch Mar Abha the Great (540—552 AD), a convert from the Magi, a great Zoroastrian teacher and secretary to the Provincial Governor until he became a Christian. A graduate (after conversion) from the Seminary at Nisibis and later professor there, and a devotee of Theodore of Mopsuestia and Diodore of Tarsus, as well as Nestorius of Constantinople, Abha I recognized the Persian Church, traveling all over Persia and taking stern measures against dissident church leaders. This was also the time when Jacob Baradeus (ca500-578) was recognizing the western Syrians (called Jacobites by the West after him); and when these latter was persecuted by the Greeks in the Byzantine empire, they also escaped in large numbers to Persia, and established a rival church (so-called Jacobite) to the Persian (so-called Nestorian).
In the century following, the rise and spread of Islam must have put the stirrup to the Church's galloping missionary activity. The Persian Church produced great leaders through its strong monastic movement and theological school. 'Nestorianism" was clearly defined by Mar Babai the Great (569-628) in his Book of the Union (i.e.union of Godhood and Manhood in Christ). with the conquest of Persia by Muslim Arabs (651 AD), the Nestorian Church was organized as a separate melet (ethnic group), recognized by the Islamic government. With the Patriarchal seat moving from Seleucia - Ctesiphon to Baghdad the cultural capital of the world (ca 775 AD) the head of the Nestorian Church comes to have considerable prestige and political power, with the title Patriarch of Baghdad.
The Nestorians expanded into China, Central Asia and India during the 6th to 8th centuries. The Christian monument of Hsi-an-Fu (with Syriac and Chinese inscriptions) speaks about Alopen's missionary Journey to China in 635 AD, and his being received gladly by Emperor TaiTsung. This 9ft high stone monument was discovered in the Chinese city of Chou-Chi in 1625, and is dated in 781 AD. Replicas of the monument can now be seen in the Metropolitan Museum of the Arts in New York, as well as in Japan. John of Monte Corvino visiting Pekin (Beijing) in 1294 AD still found a powerful Nestorian Community there. There is evidence that the Church had spread into Korea and Japan as well, well before the 13th century. The Nestorian Church spread also among the Monghols, Turks, Tartars, Tibetans. The thirteenth century episcopal lists of the Nestorian Church gives the names of the Metropolitan of the Turks (tenth in rank) with those of Java, India, Samarkhand and China following. There were many Tartar and Monghol kings who embraced the Christian faith.
Latin missionary incursions into the Nestorian Church begin with the 13th century and mark the downfall of this Church. Wherever they could, the Franciscan John of Monte Corvine, the Dominican William of Montferrat and their successors annexed small Nestorian Churches in Asia into the Roman Catholic fold. Clement V (1305-1314) who was the first "Captivity Pope" operating from Avignon with the help of the French king Philip and English King Edward I, as well as Pope John XXII (1316-1334) also Avignon-based) made laws for correcting the "errors" of the Nestorians they were annexing, along with the 'Jacobites' and others.
By 1445 there is an official Bull of Pope Eugene IV (1431-I447) the great "reunion pope" (Florence 1439), stating that Metropolitan Timothy of the Nestorians has professed the Roman Catholic faith (Hefele, Historie ds Consiles t. VII. b.p.l106), and officially giving the name "Chaldeans" to the Nestorians who embraced the Roman Catholic Church. The largest number of "Nestorians' was probably in India, who were annexed forcibly by Portuguese Archbishop Menezes at the notorious Synod of Diamper in 1599. The Chaldoens of Mesopotamia were annexed during the period from 1551 to 1662.
Protestant missions to the Nestorians begin around 1830 with the American Presbyterian, and it is joined by Anglican missions in 1835 (SPG).
Today the Nestorians are found mainly in Baghdad and Kurdistan (Iraq), in America and in India. In India the Nestorian Church was revived by Nestorian Bishop John Elias Mellus of Akra who came around 1873, and stayed on in India till 1882.
The head of the Nestorian Church today is in India there are two bishops -- Mar Aprem and Mar Paulos.