In 1453, Constantinople was conquered by the Ottoman Turks under Sultan Mehmed II, who subsequently ordered the building converted into a mosque.[27] The bells, altar, iconostasis, ambo 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. The building was a mosque from 29 May 1453 until 1931, when it was secularised.