The legends of Prester John (also Presbyter Johannes) were popular in Europe from the 12th through the 17th centuries, and told of a Christian patriarch and king said to rule over a Christian nation lost amidst the Muslims and pagans in the Orient. Written accounts of this kingdom are variegated collections of medieval popular fantasy. Prester John was reportedly a descendant of one of the Three Magi, said to be a generous ruler and a virtuous man, presiding over a realm full of riches and strange creatures, in which the Patriarch of the Saint Thomas Christians resided. His kingdom contained such marvels as the Gates of Alexander and the Fountain of Youth, and even bordered the Earthly Paradise. Among his treasures was a mirror through which every province could be seen, the fabled original from which the "speculum literature" of the late Middle Ages and Renaissance was derived, in which the prince's realms were surveyed and his duties laid out.
We also saw there at that time [Dec 1145] the aforesaid Bishop of Jabala in Syria.... He said, indeed, that not many years since, one John, a king and priest living in the Far East, beyond Persia and Armenia, and who, with his people, is a Christian, but a Nestorian, had warred upon the socalled Samiards, the brother kings of the Medes and Persians. John also attacked Ebactanus . I . the capital of their kingdom. When the aforesaid kings advanced against him with a force of Persians, Medes, and Assyrians, a threeday struggle ensued, since both sides were willing to die rather than to flee. At length, Prester John so he is usually called put the Persians to flight and emerged from the dreadful slaughter as victor. The Bishop said that the aforesaid John moved his army to aid the church of Jerusalem, but that when he came to the Tigris and was unable to take his army across it by any means, be turned aside to the north, where he had been informed that the stream was frozen solid during the winter.