‘This priest-king, of reputable phenomenal wealth and power, who was thought to reign somewhere in the East, galvanized monarchs and explorers throughout the High and Late Middle Ages up to the early Modern period just as the mythical city of El Dorado had done for the Conquistadores. The consensus, however, among medievalists is that the story seems to have originated during the twelfth century. The narrative of Prester John had the practical effect of reinforcing the religious stamina of the crusaders by holding out the promise that a fabulously rich and mighty oriental king-priest was due to march against Islam from the East in support of his fellow Christians.’