The Church of the East was established during the missionary activity of the Apostolic Age. Written records have been traced to the late second century of the Christian era. The number of people who belonged to the Church at that time, and the broad area it covered, indicates that there had been a long period of development and growth, possibly dating as far back as the first century and the time of the Apostles. Tradition dates the founding of the Church of the East to the middle of the first century.

The Church of the East first developed in the Parthian Empire, which was overthrown by the Persian empire in the third century. The Church continued to develop and spread under Persian rule. The Church spanned the region lying to the east of the Roman border, stretching as far as India. Though the exact location of the Church’s first congregations cannot be established from historical records, it is likely that it began its most serious development in the region of Kh’dayab (Adiabene) in northern Mesopotamia, from there spreading in all directions throughout the empire.

The Assyrian people of upper Mesopotamia have always been an important part of the Church of the East, though historically they were only one ethnic group among many others within the Church.

Today they represent the single surviving cultural group. Though the Church moved far beyond its beginnings in upper Mesopotamia, the language of that region (Syriac) remained the language of the Church. Its vocabulary, with a certain amount of Greek that was added in, was the source of its characteristic theological formulations.

The Church of the East is governed according to the Apostolic model of bishops, presbyters, and deacons. At the turn of the fourth century (c. AD 310) Papa bar Gaggai, the bishop of the capital city of the Persian Empire, Seleucia-Ctesiphon, organised the bishops of the Church in a form which resembled the model developed in the West. He centralised the administration of the Church under his own jurisdiction and assumed the title “Catholicos of the East.” From that time on, the bishop of the imperial capital held this office. The Catholicos became the presiding bishop over the entire Church, and his dignity and power were subsequently added to in the fifth century when he received the title “Patriarch”. This was done at a general synod called by the Catholicos, Isaac, at Seleucia-Ctesiphon in AD 410. At this synod Marutha, a representative from the Roman Emperor, brought to the assembled bishops the canons and creed of the Council of Nicaea, and they were officially approved and received by the Church of the East.

Historically, the Catholicos-Patriarch governed the general synod of the bishops. The general synod was made up of all Metropolitans (Archbishops) and Bishops. The Metropolitans were in charge of the provinces, which each contained four to eight bishops. This historic model no longer exists due to the greatly reduced numbers within the Church and the dislocations of its membership. A bishop is considered legitimate if he has been ordained into the Apostolic succession by at least two (preferably more) other bishops who are themselves properly ordained and in full communion with their fellow bishops. A bishop’s legitimacy endures only so long as he himself maintains such full communion.

The Church of the East has a sacramental system, largely resembling the sacramental systems of the Greek and Latin traditions. The Sacraments of Baptism and Eucharist are primary, while the Sacrament of Holy Orders affects the other Sacraments. Confirmation is administered with Baptism, and Absolution is a benefit of the Eucharist, though Absolution is also administered separately during a common service of Absolution, and is also administered to individuals, with penance, in the case of serious sin. The Sign of the Cross, Unction, and “Holy Leaven” are defined as additional Sacraments.

The central feature of the worship life of the Church of the East is the Eucharist, known in the Syriac language of the Church as the “Qurbana Qadisha”, or “Holy Offering”. The liturgy of the Eucharist is attributed to the Apostles, Addai and Mari, who discipled the East. The liturgy consists of a service for the catechumens and a service for the faithful. The Host is a leavened loaf, and the cup is an equal mixture of wine and water. The baptised faithful receive the Body and Blood of Christ under both species of bread and wine, and the “real presence” of Christ is understood in the elements. A priest ordained by a bishop in the apostolic succession is required for the Consecration, and a deacon is required to assist the celebrant. A community of worshipping believers must be present at the celebration.

Baptism is administered to infants of Christian families and to new converts. It is not given to those who, for whatever reasons, enter the Church from other Christian bodies and have already been baptised with a Trinitarian formula. Infant baptisms oblige parents and sponsors to rear the child in the Christian faith and to nourish him or her at the altar and within the community of faith. The Baptismal liturgy resembles the Eucharistic liturgy in form. Following an anointing with oil there is a triple immersion in consecrated water in the name of the Holy Trinity, and a final “sealing”, which is Confirmation, with the imposition of hands at the door of the altar.

Matrimony and funeral services consist largely of Psalms, anthems, and blessings. They are lengthy, colourful, and emotional occasions, and reflect ancient customs and usages.