Saint Thaddeus Monastery or Qara Kelisa is one of the three churches in this area which was registered on the UNESCO World Heritage List. The church was listed along with St. Stephanos and Dzordzor Chapel in 2008. According to the narrations, in 40 A.D, one of the apostles of Jesus named Thaddeus, came to the present region which was then part of southern Armenia, to propagate Christianity but was arrested and killed at the behest of the Armenian ruler. The monastery was built on his burial place. The monastery has been rehabilitated several times in various historical periods, most notably by Nasir al-Din al-Tusi in the Ilkhanate period and Abbas Mirza in the Qajar period.
Regarding the architecture, the church is divided into two sections, the old and the new; The old section was built using black stone, and the new section was built using white stone during the Qajar period. Like the old fortresses, Saint Thaddeus Monastery contains 5 watchtowers all around the walls.