On 27 February Turanshah, the new Sultan, arrived in Egypt from Hasankeyf and went straight to Al Mansurah to lead the Egyptian army. Ships were transported overland and dropped in the Nile (in Bahr al-Mahala) behind the ships of the crusaders cutting the reinforcement line from Damietta and besieging the crusade force of King Louis IX. The Egyptians used Greek fire and destroyed and seized many ships and supply vessels. Soon the besieged crusaders were suffering from devastating attacks, famine and disease. Some crusaders lost faith and deserted to the Muslim side.

King Louis IX proposed to the Egyptians the surrender of Damietta in exchange for Jerusalem and some towns on the Syrian coast. The Egyptians, aware of the miserable situation of the crusaders, refused the besieged king's offer. On 5 April covered by the darkness of night, the crusaders evacuated their camp and began to flee northward towards Damietta. In their panic and haste they neglected to destroy a pontoon bridge they had set over the canal. The Egyptians crossed the canal over the bridge and followed them to Fariskur where the Egyptians utterly destroyed the crusaders on 6 April. Thousands of crusaders were killed or taken prisoner. Louis IX surrendered with his two brothers Charles d'Anjou and Alphonse de Poitiers. King Louis' coif was exhibited in Syria.