 All these attempts to mount a combined offensive between the Franks and Mongols were too little and too late . In May 1291 , the city of Acre was conquered by the Egyptian Mamluks in the Siege of Acre . When Pope Nicholas IV learned of this , he wrote to Arghun , again asking him to be baptized and to fight against the Mamluks . But Arghun had died on March 10 , 1291 , and Pope Nicholas died as well in March 1292 , putting an end to their efforts towards combined action . 
