 Hulagu departed for Karakorum and left Kitbuqa , a Nestorian Christian general , to continue the Mongol conquest . Damascus capitulated after the arrival of the Mongol army , but was not sacked like other captured Muslim cities . However , from Gaza , an @-@ Nasir Yusuf managed to rally the small garrison he left in the Citadel of Damascus to rebel against the Mongol occupation . The Mongols retaliated by launching a massive artillery assault on the citadel and when it became apparent that an @-@ Nasir Yusuf was unable to relieve the city with a newly assembled army , the garrison surrendered . 
