Former Orthodox patriarchal basilica, later a mosque, and now a museum in İstanbul, Turkey. The building was a mosque from 29 May 1453 until 1931, when it was secularized. It was opened as a museum on 1 February 1935. The church contained a large collection of holy relics and featured, among other things, a 15 m silver iconostasis. In 1453, Constantinople was conquered by the Ottoman Turks under Sultan Mehmed II, who subsequently ordered the building converted into a mosque. The bells, altar, iconostasis, and sacrificial vessels were removed and many of the mosaics were plastered over. Islamic features – such as the mihrab, minbar, and four minarets – were added while in the possession of the Ottomans. It remained a mosque until 1931 when it was closed to the public for four years. It was re-opened in 1935 as a museum by the Republic of Turkey.