 Louis 's campaign against Egypt did not go well . He successfully captured Damietta , but lost his entire army at the Battle of Al Mansurah , and was himself captured by the Egyptians . His release was eventually negotiated in return for a ransom ( some of which was a loan from the Templars ) and the surrender of the city of Damietta . A few years later , in 1252 , Louis tried unsuccessfully to ally with the Egyptians , and then in 1253 he sought allies among both the Ismaili Assassins and the Mongols . When he saw a letter from Hethum 's brother , the Armenian noble Sempad , which spoke well of the Mongols , Louis dispatched the Franciscan William of Rubruck to the Mongol court . But the Mongol leader Möngke replied with only a letter via William in 1254 , asking for the King 's submission to Mongol authority . 
