Chaldean Syrian Church

Assyrian Church of the East (of India)
Founder	St. Thomas the Apostle, according to its tradition
Independence	Apostolic Era
Recognition	Church of the East
Primate	Metropolitan, Mar Aprem Mooken (under the authority of Gewargis III Catholicos-Patriarch of the Assyrian Church of the East)
Headquarters	Thrissur, Kerala, India
Territory	India
Language	Malayalam, English, Hindi, Syriac
Members	India 25,000

The Chaldean Syrian Church is an Indian Christian church which is currently an archbishopric of the Assyrian Church of the East. Its members are a part of the St. Thomas Christian community, who trace their origins to the evangelical activities of Thomas the Apostle in the 1st century. They are almost exclusively based in the state of Kerala, with the church's cathedral located in Thrissur. Despite carrying the "Chaldean" title in its name, the church is unrelated to the Chaldean Catholic Church of the Middle East, an Eastern Catholic church in communion with the Pope.

The Chaldean Syrian church is the modern day continuation of the East Syrian Rite Assyrian Church of the East in India, after the majority of its followers were converted to Catholicism or West Syrian Rite Churches. The Church of the East controlled the entire area up until 1599, when the Autonomous East Syrian Indian Church was subjugated by the Portuguese and forced to follow Catholic doctrines due to the Synod of Diamper, in addition to the destruction of all their existing holy books and getting cut off from the Assyrian Church of the East. However, when a new patriarch was elected a few decades later named Mar Thoma I, the Coonan Cross Oath of 1653 was made stating that the Church of India would break off from the Catholic Church. This was largely because a request for reunification with the Church of the East in the Middle East was declined, resulting in a bishop who was to reunite the churches named Ahatallah being tortured and killed by the Portuguese in 1652. As a result, Thoma formed his own independent church and waited for a bishop from the Assyrian Church of the East to come and officially reunite them. However, unbeknownst to him, a Syriac Bishop came, and because he unknowingly thought he was an Assyrian Bishop, ended up allowing the Syriac Bishop to unite the Indian Church with the west Syrian Rite Syriac Orthodox Church, forming the Malankara Orthodox Syrian Church. Soon after, Many members of that church joined a Portuguese sponsored Church known as the Syro-Malabar Catholic Church that implemented reforms in an effort to make them return. However, some of the members of Mar Thomas Church knew the Syriac Bishop was not of the East Syrian rite, and waited for a Bishop to come from the Assyrian Church of the East. When Mar Gabriel, The Assyrian bishop finally arrived in 1701 the Chaldean Syrian Church was established, and broke off from the Syro-Malabar Catholic Church which they joined temporarily. Later, in the 1890s, the Syro Malabar Catholic Church had reforms which restored various Assyrian practices destroyed after the Synod of Diamaper, restoring the Syro Malabar Catholic Church to an East Syrian rite Oriental Catholic church, Similar to the Chaldean Catholic Church.

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