Église apostolique assyrienne de l'Orient
The Church of the East is that ancient church which developed in the regions of Assyria, Babylonia, and Persia (today's Iraq and western Iran), to the east of the Roman-Byzantine empire. It is an Apostolic church, established by the apostles St Thomas, St Thaddeus, and St Bartholomew. St Peter, the chief of the apostles added his blessing to the Church of the East at the time of his visit to the see at Babylon, in the earliest days of the church: "... The chosen church which is at Babylon, and Mark, my son, salute you ... greet one another with a holy kiss ..." ( I Peter 5:13-14). During the first century of the Christian era, the Church of the East was established in the city of Edessa, in the northern-most Aramaic-speaking city-state of the eastern region. Reference to this can be found in the writings of the historian Eusebius (Ecclesiastical History; bk 1, ch 13). In 280, the Church of the East was officially organized under the Catholicos-Patriarch Mar Papa bar Gaggai of Seleucia-Ctesiphon, and in 410 it renounced all subjection to the see of Antioch. The eastward movement of the church saw Christian communities flourishing in what is now Afghanistan and south-central Asia.
Many churches were established along the Tigris and Euphrates rivers, following the "silk and spice route" of the ancient caravans. The great subcontinent of India was evangelized by Thomas the apostle. By the end of the 3rd century, 19 episcopal see cities existed, with their bishops spiritually governing the faithful in the holy tradition of the apostles and their teachings.
The Church of the East suffered persecution at the hands of the Persians, because of the hostility between the Persian empire and the Roman-Byzantine empire which had adopted Christianity. The church was and remained a minority in Persia, but was large and active, and noted for its scholastic achievements, its monastic centres, its martyrs and teachers. The pressure of persecution favoured expansion to the east. Missionaries from the Church of the East spread into the Asian continent, proclaiming the message of Jesus Christ in the far off regions of the Mongol tribes. In the 7th century they made their way into China. The so-called "Nestorian Tablet" found in Xi'an witnesses to this early Christian presence in China.
The Muslim conquest beginning in the 7th century affected the church and brought new persecutions. The Mongol khans who had been open to Christianity came under the influence of Islam and turned against the church during their invasions of the Arabian peninsula. Many Christians were killed or forced to convert to Islam. The Church of the East withdrew into the Hakkari mountains (today's northern Iraq and eastern Turkey) which became the home of the patriarchal see, and where it remained in isolation for centuries. When the British established their rule in Iraq after World War I, the patriarch was exiled to Cyprus. Eventually he moved to the USA, when it became evident that the Iraqi authorities would not let him return to his people.
The Church of the East is now thinly spread throughout the world, with its main centres in Iraq, Iran, Syria, India (where it is known as the Chaldean Syrian church), North America, Australia, New Zealand and Europe. It has archdioceses for Iraq and Russia, India, Lebanon and Europe, three dioceses in the USA and one each in Syria, Iran, Canada, Europe, Australia and New Zealand. The Catholicos-Patriarch resides in the USA.
The Assyrian Church was represented at the Council of Nicea in 325. The Nicene Creed is the universally received faith of the church. With regard to the teaching of Nestorius, the Church of the East maintains that Jesus Christ is Son of God and Son of Man, two qnome united in one Sonship. All the documents of the church are in Aramaic, utilizing the Nestorian Syriac script. The sacred rites of the Church of the East include the pre-431 rite of Addai and Mari, together with other texts.
In the 16th century a split occurred in the Church of the East. A part of the church which became known as the Chaldean Catholic Church joined the Roman Catholic Church. Another, smaller group separated in the second half of the 20th century and took the name Ancient Church of the East, under its own patriarch who resides in Baghdad.