St. Thaddeus Cathedral is located 15km northeast of the town Chaldoran, near the village of Qara-Kelissa, which is why the cathedral is also known as Qara-Kelissa (“Black Church” in Turkish) to the locals. Besides being a religious site with a particular significance among Iranian Armenians, this large church was built between the fourth and sixth centuries AD on the grave of St. Thaddeus, one of the apostles of Jesus Christ who was martyred in the year 48 AD for his advocacy of the Christian Faith. The church, which is situated in the Qara-Kelissa village, one of the districts of Siah-Cheshmeh in Maku, is the final resting place of St. Thaddeus. According to the Armenian historical references, the Armenians of the Sassanid period were mainly Zoroastrians, although a scattered group of them followed the Mithraean principle. In the year 43 AD, two of Jesus Christ’s evangelists named Thaddeus (also known as Jude Thaddeus or Jude Labbeus) and Bartholomew crossed the Northern Mesopotamia for the first time and settled in Ardaz, capital of Armenian Empire. Heedless to the orders of Sanaduk, the Zoroastrian King of Armenia, they started a campaign to advocate Christianity. As a result, 3500 people including the King’s daughter named Sanadukht converted to the Christian faith. To stop them from further spreading Christianity, the Armenian King gave order for a mass elimination of Christians. All Christian Armenians including the King’s own daughter were killed in the massacre and buried at the present location of Qara-Kelissa and its surrounding area. Armenians claim that the St. Thaddeus Cathedral is the first church in the world made to order by the apostles and evangelists of Jesus Christ. Based on their religious beliefs, martyrdom is the ultimate bliss for any man, and so, a special ceremony is held at Qara-Kelissa during the second half of July each year to commemorate the martyrdom of St. Thaddeus and his Christian followers.