The citadel was expanded between 1537 and 1541 by the Ottoman sultan Suleiman the Magnificent, whose architects designed a large entrance, behind which stood a cannon emplacement. For 400 years, the citadel served as a garrison for Turkish troops. The Ottomans also installed a mosque near the southwest corner of the citadel commonly known as the Mihrab el-Qal'a ed-Dawood ("Prayer niche of David's fortress"), erecting a minaret during the years 1635-1655. In the 19th century the conspicuous minaret, which still stands today, became commonly referred to as the "Tower of David". At least two mosques are known to exist within the Jerusalem Citadel.
