Kalenderhane Mosque,  Istanbul

Kalenderhane Mosque is a former Eastern Orthodox church in Istanbul, converted into a mosque by the Ottomans. With high probability the church was originally dedicated to the Theotokos Kyriotissa. This building represents one among the few extant examples of a Byzantine church with domed Greek cross plan. The mosque is located in the Fatih district of Istanbul, Turkey, in the neighborhood of Vefa, and lies immediately to the south of the easternmost extant section of the aqueduct of Valens, and less than one km to the southeast of the Vefa Kilise Mosque. The building has a central Greek Cross plan with deep barrel vaults over the arms, and is surmounted by a dome with 16 ribs. The structure has a typically middle Byzantine brickwork with alternating layers of brick and stone masonry. The sanctuary is on the east side; however, the reconstructed mihrab and minbar are in a corner to obtain the proper alignment with Mecca. As a whole, the mosque of Kalenderhane represents together with the Gul Mosque in Istanbul, the Church of Hagia Sophia in Thessaloniki and the Church of the Dormition in (Koimesis) in Iznik (Nicaea), one of the main architectural examples of a domed Greek ross church from the Byzantine middle period.  (Source: en.wikipedia.org)