Several attempts at a Franco-Mongol alliance against the Islamic caliphates, their common enemy, were made by various leaders among the Frankish Crusaders and the Mongol Empire in the 13th century. Such an alliance might have seemed an obvious choice: the Mongols were already sympathetic to Christianity, given the presence of many influential Nestorian Christians in the Mongol court. The Franks—Western Europeans, and those in the Levantine Crusader states—were open to the idea of support from the East, in part owing to the long-running legend of the mythical Prester John, an Eastern king in an Eastern kingdom who many believed would one day come to the assistance of the Crusaders in the Holy Land. The Franks and Mongols also shared a common enemy in the Muslims. However, despite many messages, gifts, and emissaries over the course of several decades, the often-proposed alliance never came to fruition.

Prester John was a legendary Christian patriarch, presbyter, and king. Stories popular in Europe in the 12th to the 17th centuries told of a Church of the East patriarch and king who was said to rule over a Christian nation lost amid the pagans and Muslims in the Orient. The accounts were often embellished with various tropes of medieval popular fantasy, depicting Prester John as a descendant of the Three Magi, ruling a kingdom full of riches, marvels, and strange creatures.