Prester John, the name given in the Middle Ages to a supposed Christian king and priest of great power and splendour. Otto, Bishop of Freisingen, makes him conquer the Persians and Medes in a great battle and attempt to reach Jerusalem. About 1165 a letter from "Presbyter Joannes" to Manuel, Emperor of the East, was circulated throughout Europe. Of this letter nearly 100 MSS. exist. In 1177 an epistle seems to have been written by Pope Alexander III. from Venice to "John, the illustrious and magnificent king of the Indies," regarding the establishment of ti church and altar at Jerusalem. Gibbon and other writers make the subject of the first of these letters Gur Khan, the king of Khitai or Cathay, who, however, was probably not a Christian; while the great Mongol conqueror Genghiz Khan is probably to be identified with later bearers of the name. Prester John's realm was at first supposed to.be in Central Asia, but from the 14th century onwards it was placed in Africa, and he becomes thus almost certainly identical with the king of Abyssinia, who was a Christian.