sentences:  After the Ottoman conquest of Constantinople in 1453, the church remained untouched until the reign of Bayezid II.Then (between 1506 and 1513) it was transformed into a mosque by Hüseyin Ağa, the Chief Black Eunuch, custodian of the "Bab-ı-Saadet" (literally "The Gate of Felicity" in Ottoman Turkish) in the Sultan's residence, the Topkapı Palace.At that time the portico and madrasah were added to the church.