41°01′45″N 28°56′23″E / 41.029071°N 28.939828°E / 41.029071; 28.939828 The Odalar Mosque (Turkish: Odalar Câmîi, meaning "the mosque of the barracks" after the nearby accommodations of the married Janissaries established in this quarter in the 18th century. Also: Kemankeş Mustafa Paşa Câmîi) was an Ottoman mosque in Istanbul. The building was originally a Byzantine-era Eastern Orthodox church of unknown dedication. In 1475, after the Fall of Constantinople (1453), it became a Roman Catholic church, dedicated to Saint Mary of Constantinople, until finally it was converted into a mosque by the Ottomans in 1640. The mosque was destroyed by fire in 1919, and since then has fallen into ruin. As of 2011, only some walls remain, hidden among modern buildings.

The ruins of the building lie in Istanbul, in the district of Fatih, in the neighborhood of Salmatomruk, not far from Edirne Kapı (the ancient Gate of Charisius), more or less halfway between the Chora Church and the Fethiye Mosque. The few remains lie in a courtyard and can be accessed through modern blocks built on Müftu Sokaĝi 20-22.

Between the ninth and the tenth century a church with an underlying basement and a crypt was erected on the top of the sixth hill of Constantinople, on a plateau which is limited by the open air cistern of Aetius (now a football field) and by the unidentified Byzantine edifice denominated in Ottoman times as Boĝdan Saray. The dedication of this building is uncertain, but it was probably part of a complex which also included today's Kasım Ağa Mosque and the İpek Cistern, and was almost certainly the katholikon of a monastery.

The edifice has been identified for a long time as the Theotokos en te Petra, but without conclusive evidence. During the Byzantine period, several monasteries lay in the area; the Monastery of Manuel, that devoted to St. John in Petra, and the Kecharitomene nunnery ("full of grace" or "favoured (by God)"). The latter was founded at the beginning of the 12th century by Empress Eirene Doukaina, and is known above all because of its detailed and extant typikon. The nearby church of the Theotokos tes Kellararias, used by the nuns of the Kecharitomene as a burial place, and that of Hagios Nikolaos, both mentioned in the typikon of the nunnery, are possible candidates for the identification. Moreover, the Odalar Mosque could also be identified with a nearby church dedicated to Saints Sergius and Bacchus, which lay "near the cistern of Aetios": not to be confounded with the homonymous church which lies near Hagia Sophia) because of the discovery in the vicinity of a monogrammed capital (unfortunately found not in situ). Between 1150 and 1175 a new church of the cross-in-square plan was built above the old one (possibly destroyed by fire or menaced by a landslide).

The documented history of the edifice begins in 1475, shortly after the Fall of Constantinople, when Sultan Mehmed II conquered the Genoese colony of Caffa, in Crimea. About 40,000 Latin, Greek, Armenian and Jewish inhabitants who lived in Caffa ("Caffariotes" or, in Turkish, Kefeli) were then deported to Istanbul and relocated to this quarter, which was named after them Kefe Mahallesi. The Latins, mainly Genoese, were authorized to use in their quarter as churches the building and, together with the Armenians, another edifice known later as Kefeli Mosque, which was dedicated to Saint Nicholas.

The edifice, dedicated then to Saint Mary of Constantinople (Italian: Santa Maria di Costantinopoli), was officiated by the Dominicans, which before the Ottoman conquest had also a monastery in the city on the Black Sea. Here was brought from Caffa a large icon of the Hodegetria type, which now is kept in the Dominican monastery of SS. Peter and Paul in Galata. Due to all that, at the beginning of the sixteenth century the church of Saint Mary had turned into the center of this quarter predominantly inhabited by Italians, but the building fell soon in disrepair. Under Sultan Murad IV (r. 1623–1640) the decision was taken to exclude from the walled city the Christians who were not Ottoman subjects and to resettle them in Galata and Pera. As a consequence, and after riots between Christian and Muslims, the church was closed in 1636, and in 1640 it was transformed into a mosque by Sadrazam (Grand Vizier) Kemankeş Mustafa Pasha (d. 1644). As mentioned above, only the Hodegetria Icon could be moved with great difficulties to Galata.

After the relocation of the married Janissaries in the quarter in 1782, the mosque got the appellation of Odalar (In Turkish "Oda" means "room" but also "barrack of the Janissaries"). Previously these were lodged at the Eski Odalar ("Old Barracks") near Şehzade Mosque, which were destroyed in the fire of 1782. The building decayed steadily (by the mid-19th century the dome had collapsed), and it was heavily damaged by the fire of Salmatomruk on 2 July 1919. When the quarter was rebuilt with modern criteria the edifice was not restored, and fell into ruin.

As mentioned above, several constructive phases can be recognized in the building during the Byzantine period. The first church, erected in the middle Byzantine age, had an almost square plan (about 11.65 m x 10 m ) with three apses, and was oriented toward the East. In 1935, only the tripartite sanctuary and the Bema were still visible. The church was built on a basement composed of 24 vaulted rooms and a vaulted crypt with an apse, which is supposed to have been a chapel containing relics. These rooms had at first a profane usage, later they were used as burial place and finally as a cistern.