Christianity has a long history in Iran, which dates back to the early years of the faith. It has always been a minority religion. The history of the Catholic Church in Iran began in the thirteenth century with the arrival of some Dominican friars in the northwest of the country.
The introduction of Christianity was favored by the Mongol khans, which dominated the country at the time. The first Catholic hierarchy was established in 1318: on April 1 of that year, with the Redemptor noster bull, Pope John XXII he erected the Archdiocese of Soltaniyeh, to which he joined six suffragan bishops. The Catholic Church represents one of the oldest Christian communities in Iran, although Catholics in the country are only a small minority: as of December 31, 2005, out of 69 million Iranians, there were 24.565 Catholics, or 0,035% of the population total. Christianization in Persia was the work of the Eastern Church, an autocephalous church and not in communion with catholicity.
In 1976, the census reported that the Christian population numbered 168.593 people, most of them Armenians. Due to the Iran-Iraq war in 1980 and the dissolution of the Soviet Union in 1990, almost half of Armenians migrated to the newly independent Republic of Armenia; the opposite trend occurred from 2000 onwards, and the number of Christians with Iranian citizenship increased to 109.415 in 2006. At the same time, a significant immigration of Assyrians from Iraq was recorded due to the massacres and harassment that occurred in post-Saddam Iraq. However, most of these new migrants do not have Iranian citizenship.
In 2008, the central office of the International Union of Assyrians was officially transferred to Iran after being hosted in the United States for more than four decades. Christians in Iran mainly live in the capital Tehran and in the cities of Isfahan and Shiraz. Today, there are at least 600 churches for 300.000 - 370.000 Christians in Iran.