The Assyrian Apostolic Church considers its origins in the missionary activity of the Apostle Thomas and the Lord's disciple Addai. However, the first Christian congregations did not emerge until the third century in the Persian Empire. While the Assyrian Apostolic Church was one of the largest Christian communities in the world in the Middle Ages, today it is one of the smallest Eastern Church denominations. A part of the Eastern Syrian Christians decided for a union with Rome, from which the Chaldean Church finally emerged. The rite of the Assyrian Apostolic Church is Eastern Syrian, while the festivals and holidays are in accordance with Gregorian tradition. The members of the Assyrian Apostolic Church today are not in the Middle East as they once were, but are mostly scattered in the Diaspora. Head of the Assyrian Apostolic Church is Patriarch Gewargis Sliva. In Germany there are two parishes in Wiesbaden/Mainz.

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