In 1144, Zengi conquered Edessa, a crusader stronghold, which led to a new crusade from Europe in 1148. In the meantime Zengi was assassinated and his territory was divided among his sons, one of whom, Nur ad-Din, emir of Aleppo, made an alliance with Damascus. When the European crusaders arrived, they and the nobles of Jerusalem agreed to attack Damascus. Their siege, however, was a complete failure. When the city seemed to be on the verge of collapse, the crusader army suddenly moved against another section of the walls, and were driven back. By 1154, Damascus was firmly under Nur ad-Din's control.