 Zengi later appointed Ayyub governor of Baalbek, and when the town was besieged in 1146 by Mu'in ad-Din Unur, the atabeg of the Burid emir of Damascus, Ayyub surrendered Baalbek and retired to Damascus.Shirkuh, meanwhile, entered the service of Zengi's son Nur ad-Din Zengi, who had designs on Damascus; when the Second Crusade besieged the city in 1148, Nur ad-Din forced Mu'in ad-Din and the Burids into a reluctant alliance.Soon Nur ad-Din demanded the city be handed over to him, and Ayyub and Shirkuh negotiated its surrender in 1154.