During the Fifth Crusade (1213–1221), as the Christians were unsuccessfully laying siege to the Egyptian city of Damietta, the legend of Prester John became conflated with the reality of Genghis Khan's rapidly expanding empire. Mongol raiding parties were beginning to invade the eastern Islamic world, in Transoxania and Persia in 1219–1221. Rumors circulated among the Crusaders that a "Christian king of the Indies", a King David who was either Prester John or one of his descendants, had been attacking Muslims in the East and was on his way to help the Christians in their crusades. In a letter dated , Pope Honorius III even commented about "forces coming from the Far East to rescue the Holy Land".