Church of the East in India

According to apocryphal records, Christianity in India and in Pakistan (included prior to the Partition) commenced in 52 AD, with the arrival of Thomas the Apostle in Kodungallur (Cranganore). Subsequently, the Christians of the Malabar region, known as St Thomas Christians established close ties with the Levantine Christians of the Near East. They eventually coalesced into the Church of the East led by the Catholicos-Patriarch of Seleucia-Ctesiphon.

The Church of the East was often separated from the other ancient churches due to its presence in the Assyrian-Parthian Empire, an ancient rival of the (Byzantine) Greek and (Latin) Roman Empires. When Archbishop Nestorius of Constantinople was declared a heretic by the Council of Ephesus, the Church of the East refused to acknowledge his deposition because he held the same christological position. Later, the "anaphora of Mar Nestorius" came to be used by Church of the East, which for this reason has been pejoratively labelled the "Nestorian Church" by its theological opponents.

When the Portuguese Inquisition in Goa and Bombay was established in the 16th century, they opposed the East Syriac rite of Christian worship in what was Portuguese Cochin. After the schism of 1552, a section of the Church of the East became part of the Chaldean Catholic Church, both the Assyrian and Chaldean patriarchates intermittently attempted to regain their following in the Indian subcontinent, by sending their prelates to the Malabarese Christians. The Vatican supported the claim of the bishop from the Chaldean Church of Ctesiphon. But the Portugal-sponsored Synod of Diamper in 1599, overseen by Aleixo de Menezes, the Portuguese Archbishop of Goa, replaced the East Syriac bishop of St Thomas Christians and placed them under the Portuguese Padroado-backed bishop. After that any attempts of Thomas Christians to contact bishops, even Chaldean Catholic ones in the Middle East were foiled.