De Sonnac's next engagement was at the Battle of Mansurah, for the city containing the area's defensive force, the last obstacle to central Egypt. The Muslims had been protected by the swollen Nile, but on 8 February 1250, a local Bedouin showed them where they could cross. De Sonnac, Robert of Artois, the King's brother and William II Longespee, leader of the English troops, launched an assault on the Muslim force without the main Frankish army. Taken by surprise, the Egyptians quickly retreated from the riverbank into the city and the Count foolishly gave chase, outnumbered and with no back-up from the bulk of the French forces.