As early as the 13th century, Catholic missionaries – primarily Dominicans and Franciscans – had been active among the faithful of the Assyrian Church of the East. This resulted in a series of individual conversions of bishops and brief unions, but no permanent community was formed.

In the mid-15th century a tradition of hereditary patriarchal succession (passing from uncle to nephew) took effect in the Assyrian church. As a result, one family dominated the church, and untrained minors were being elected to the patriarchal throne.

When such a patriarch was elected in 1552, a group of Assyrian bishops refused to accept him and decided to seek union with Rome. They elected the reluctant abbot of a monastery, Yuhannan Sulaka, as their own patriarch and sent him to Rome to arrange a union with the Catholic Church. In early 1553 Pope Julius III proclaimed him Patriarch Simon VIII "of the Chaldeans" and ordained him a bishop in St. Peter's Basilica on April 9, 1553.

The new Patriarch returned to his homeland in late 1553 and began to initiate a series of reforms. But opposition, led by the rival Assyrian Patriarch, was strong. Simon was soon captured by the pasha of Amadya, tortured and executed in January 1555. Eventually Sulaka's group returned to the Assyrian Church of the East, but for over 200 years, there was much turmoil and changing of sides as the pro- and anti-Catholic parties struggled with one another. The situation finally stabilized only on July 5, 1830, when Pope Pius VIII confirmed Metropolitan John Hormizdas as head of all Chaldean Catholics, with the title of Patriarch of Babylon of the Chaldeans, with his see in Mosul.

The Chaldean Catholics suffered heavily from massacres during World War I (1918) when four bishops, many priests, and about 70,000 faithful died.

The location of the Patriarchate shifted back and forth among several places over the centuries, but gained a measure of stability after it was set up at Mosul in 1830. In 1950 it moved to its present location in Baghdad after substantial migration of Chaldean Catholics from northern Iraq to the capital city.

The Chaldean Catholic Church's relationship with the Assyrian Church of the East improved dramatically after the signing of a joint christological agreement between the Pope and the Assyrian Patriarch in Rome in November 1994. In August 1997 the Holy Synods of the two churches formally instituted a commission for dialogue to discuss pastoral cooperation at all levels [see Assyrian Church of the East].

Chaldean candidates for the priesthood study at St. Peter's Patriarchal Seminary in Baghdad. In 1991 the Chaldean Holy Synod established Babel College for Philosophy and Theology next to St. Peter's Seminary. It aims to provide a higher scientific education for priests, monks, nuns and interested lay people, and is affiliated with the Pontifical Urban University in Rome. Today the largest concentration of these Catholics remains in Baghdad. There are ten Chaldean dioceses in Iraq, four in Iran, and four others in the Middle East.

The Chaldean liturgy can be traced back to the Syriac Christian culture of Edessa, and attained its present basic structure in the 7th century. The liturgical language is Syriac, and a number of Latin customs have been adopted.

The war in Iraq that has been in progress since 2003 has dealt a heavy blow to the Chaldean Catholic community there. In 2007 Patriarch Emmanuel III said that large number of Chaldeans had left Iraq because of various forms of persecution. He spoke of internal persecution by Muslim extremists who were chasing Christians out of their homes and lands, and external persecution by the occupying armies. He cited in particular the decision by American troops to transform Babel College into a military base against the wishes of the Patriarchate.

There are two Chaldean Catholic dioceses in the United States. The Eparchy of St. Thomas the Apostle of the Chaldeans was established in 1982, and is under the leadership of Bishop Ibrahim Ibrahim (25585 Berg Road, Southfield, Michigan 48034). It has five parishes in the Detroit area and two in Chicago. The Eparchy of St. Peter the Apostle of the Chaldeans in San Diego (established in 2002) has six parishes in California and one in Arizona, and is headed by Bishop Sarhad Jammo (1627 Jamacha Way, El Cajon, California 92019). In 2006 a new eparchy of Saint Thomas the Apostle of Sydney was established for Chaldeans in Australia and New Zealand, led by Bishop Djibrail Kassab. There are eight worshipping communities for approximately 29,000 Chaldeans in the two countries. In other areas of the world, Chaldeans are under spiritual supervision of the local Latin ordinaries.

Location: Iraq, Iran, Syria, Lebanon, Turkey, Israel, Egypt, France, USA
Head: Patriarch Louis Raphael I Sako (born 1948, elected 2013)
Title: Patriarch of Babylon of the Chaldeans
Residence: Baghdad, Iraq
Membership: 419,000

Last Modified: 06 Feb 2013