 Without support from the Europeans , some Franks in Outremer , particularly the Knights Hospitaller of the fortress of Marqab , and to some extent the Franks of Cyprus and Antioch , attempted to join in combined operations with the Mongols in 1280 – 1281 . The death of the Egyptian leader Baibars in 1277 led to disorganization in the Muslim territories , making conditions ripe for a new action by other factions in the Holy Land . The Mongols seized the opportunity , organized a new invasion of Syria , and in September 1280 occupied Bagras and Darbsak , followed by Aleppo on October 20 . The Mongol leader Abaqa , taking advantage of his momentum , sent envoys to Edward I of England , the Franks of Acre , King Hugh of Cyprus , and Bohemond VII of Tripoli ( son of Bohemond VI ) , requesting their support for the campaign . But the Crusaders were not organized enough themselves to be of much help . In Acre , the Patriarch 's Vicar replied that the city was suffering from hunger , and that the king of Jerusalem was already embroiled in another war . Local Knights Hospitaller from Marqab ( in the area which had previously been Antioch / Tripoli ) were able to make raids into the Beqaa Valley , as far as the Mamluk @-@ held Krak des Chevaliers in 1280 and 1281 . Hugh and Bohemond of Antioch mobilized their armies , but their forces were prevented from joining those of the Mongols by Baibars ' successor , the new Egyptian Sultan Qalawun . He advanced north from Egypt in March 1281 , positioned his own army between the Franks and Mongols , and then further divided the potential allies by renewing a truce with the Barons of Acre on May 3 , 1281 , extending it for another ten years and ten months ( a truce he would later breach ) . He also renewed a second 10 @-@ year truce with Bohemond VII of Tripoli on July 16 , 1281 , and affirmed pilgrim access to Jerusalem . 
