The Tower of David, also known as the Jerusalem Citadel, is an ancient citadel located in the Old City of Jerusalem. It was founded in 150 BC as the Old City expanded, and King Herod the Great added three massive towers to the fortifications from 37 to 34 BC. During the First Jewish-Roman War, Simon Bar Giora made the Tower his residence, and, even after the Fall of Jerusalem to the Roman Army, the Romans preserved the three towers to remind the locals of the obstacles they overcame, and they used the Tower of David as a barracks. When the Eastern Roman Empire adopted Christianity as the state religion, the Tower of David became home to a community of monks, and the Byzantines named the hill the "Tower of David" after misidentifying it at Mount Zion, King David's old palace. After the Arab conquest of Jerusalem in 638 AD, the new Muslim rulers refurbished the citadel, and it withstood the assault of the Crusaders in 1099 and surrendered only when its defenders were guaranteed safe passage out of the city. The newly erected palace of the Kingdom of Jerusalem was built south of the citadel. In 1187, the Ayyubid Egyptian sultan Saladin captured the city and its citadel, and, in 1239, the Ayyubid prince an-Nasir Dawud attacked the Crusader garrison and destroyed the citadel. In 1244, the Khwarezmians banished the Crusaders from the citadel for the last time and destroyed the entire city in the process, and the Mamluks destroyed the citadel in 1260. In 1310, the citadel was rebuilt by the Mamluk sultan an-Nasir Muhammad, and it was expanded from 1537 to 1541 by the Ottoman sultan Suleiman the Magnificent. For 400 years, the citadel served as a garrison for Turkish troops, and a minaret was erected from 1635 to 1655, as were two mosques. During World War I, the British Army captured Jerusalem amid the Sinai and Palestine campaign, and Edmund Allenby proclaimed the city's capture from the citadel. In the 1930s, a Palestinian folklore museum was opened in the citadel, but, from 1948 to 1967, the Israeli military used the Tower of David as a barracks, before returning it to its cultural position following the end of the Six-Day War. In 1989, a large history museum was opened at the Tower, examining archaeological ruins dating back 2,700 years.