In 1163 King Amalric I of Jerusalem led an invasion of Egypt, leaving the crusader states open to attack from the east. Nur ad-Din took advantage of this to invade Tripoli, but he was taken by surprise by a large combination of enemies at the Battle of al-Buqaia and was almost killed himself. He then moved north to Antioch, with assistance from his brother Qutb ad-Din in Mosul, his other vassals from Aleppo and Damascus, and the Ortoqids of the Jazira, and besieged the fortress of Harim (Harenc) in 1164. As William of Tyre says, "he stationed his engines around it in the customary manner and began to assault the place with a fury which permitted the inhabitants no rest."