Kalenderhane Mosque (Kalenderhane Camii) is one of the Byzantine churches that was converted into a mosque after the conquest of Constantinople by the Ottomans in 1453, such as Hagia Sophia, Zeyrek Mosque (Pantokrator Monastery), or Fethiye Mosque (Pammakaristos Church). It was dedicated to Virgin Mary and is very probable that its name of the church was the Church of Theotokos Kyriotissa, meaning Virgin the mother of God.
Built on top of a fifth or sixth-century Roman bath complex, the Church of Theotokos Kyriotissa was built in the twelfth century during the Komnenian Dynasty and functioned as a Greek Orthodox Byzantine church until 1453. In 1453, after the conquest of Constantinople, the church was assigned to the Kalenderi Dervishes and they used the structure as a zaviye (Islamic religious school) and imaret (soup kitchen).
In 1746, Hacı Beşir Ağa - chief eunuch of the Topkapı Palace in the first half of the eighteenth century - converted it into a mosque by adding mihrab, minbar, and mahfil. The structure was restored several times due to the fires took place in the late nineteenth century, yet it still functions as a mosque.
Kalenderhane Mosque has a Greek Cross plan supported by a dome within sixteen ribs. The medium of the structure is a typical middle Byzantine architecture, which is the combination of layers of brick and stone masonry.
After the Latin Conquest of Constantinople by the Fourth Crusader in 1204, the church was used by the Catholic Crusaders as a Roman Catholic Church and they decorated the southern chapel of the church with the frescoes portraying the life of St. Francis. Today, the frescoes can be seen at the second floor of the Istanbul Archaeological Museums.
The easiest way to get there is to take M2 Metro and get off at Vezneciler metro station. Kalenderhane Mosque (Kalenderhane Camii) is just next to the Vezneciler Metro Station.
Located in the center of historical peninsula of Istanbul in Vezneciler, Kalenderhane Mosque (Kalenderhane Camii) is also close to important landmarks of Istanbul including Pantokrator Monastery (Zeyrek Mosque), Valens Aqueduct (Bozdoğan Kemeri), Şehzade Mosque, Vefa Church Mosque (Vefa Kilise Camii), and historical Vefa Boza Shop.