Zengi, the atabeg of Aleppo and Mosul, attacked Damascus in 1135 and again in 1140. Zengi's second attack was thwarted because Damascus forged a coalition with the Crusader states to the south, arguing that if Damascus were conquered, these states would fall as well. Crusader armies attacked Damascus a third time in 1148 during the Second Crusade. This siege of Damascus ended within a week when an army led by Nur ad-Din Zangi, ruler of Aleppo and the son of Zengi, threatened the besieging Crusaders, forcing them to withdraw. After unsuccessful attacks in 1150 and 1151, Nur ad-Din finally captured Damascus in 1154. The citadel was only surrendered to Nur ad-Din after Mujir ad-Din Abaq, the last Burid ruler, had been given safe passage and lordship over the city of Homs.