The Church of Theotokos Kyriotissa (now Kalenderhane Mosque) is located near the east end of the Aqueduct of Valens in Constantinople. While it is a large Middle Byzantine church with a cross-in-square plan covered by a dome, it has a complex structural history, with several stages of building on the site, including a bath complex. 
It has peculiarities in its plan due to the inclusion of earlier structures, especially in the western and eastern ends. Most of the currently existing main church dates to the late 12th century. The earliest structure is a 4th-5th century bath. It consisted of three rooms, one consists of a rectangular forechamber leading a larger trefoil chamber, while the second and third rooms consists a circular chamber. The second structure (the North Church) is an early Byzantine basilica, dating to the 6th century. While most of the structure is speculative, its apse largely survived and became the prosthesis of the main church. It seems that it was linked to the rooms of the bath. Another church (the Bema Church) was built on the site around the bema in the 7th century. Its central apse was preserved and used as the central apse of the main church. The diakonikon consists of two chapels (the Francis Chapel and Melismos Chapel) built perhaps in the Middle Byzantine period, before the Main Church was built. The masonry of the Francis Chapel shared features of the 10th century Theotokos Church of Constantine Lips, while the Melismos Chapel is in recessed brick technique, which generally took place in the eleventh or twelfth centuries.
The Main Church, built around 1200, is a large church that incorporated the older structures within it. It has cross-in-square plan covered by a dome. Its naos is around 19 square meters, while its dome has a 8 meter diameter and rests on four massive piers that create four isolated corner compartments. The building has a narthex and exonarthex. It once had outer aisles that flanked the naos on the north and south sides along with a porch and perhaps a tower at the northwest corner. Polychrome marble revetments dominate the interior of the naos. However less than a third of the 12th century survive and the remaining wall surfaces were covered either with secondary revetment or with painted plaster imitating marble.
The St. Francis fresco cycle suggests that members of a Franciscan community were installed at the Kyriotissa during the Latin occupation of Constantinople. Although no historical evidence documents a Franciscan convent at the site of Kalenderhane, Franciscans had settled in Constantinople from 1220. During the Palaiologan period, it was at least partially redecorated. The church was converted into mosque after the conquest of the city by by Mehmed II. Its name derives from the kalenderi dervishes who used it as a mevlevihane (sufi lodge).