To such marvels in the early versions of the _Letter of Prester John_ were added others in the course of the thirteenth century and later middle ages:--the huge man-eating ants who mined gold by night;[744] the land where men lived on manna, a substance which we shall find somewhat similarly mentioned by Michael Scot and Thomas of Cantimpré;[745] the tale, which we shall also hear from Roger Bacon, of men who tame flying dragons by their incantations and magic, saddle and bridle them, and ride them through the air;[746] the five marvelous stones that froze or heated or reduced to an even state of temperature or made light or dark everything within a radius of five miles; the second five stones, of which two were unconsecrated and turned water to milk or wine, while three were consecrated and would respectively cause fish to congregate, wild beasts to follow one, and, sprinkled with hot lion’s blood, produce a conflagration which could only be quenched by sprinkling the stone with hot dragon’s blood;[747] the marvelous mill operated by the occult virtue of the stone adamant;[748] the wonderful tree on which the wonderful healing apple grew;[749] the marvelous chapel of glass, always just big enough for as many persons as entered it;[750] and the stone and the fountain that served as fireless heaters.[751] In another case a marvel is wrought by stone and fountain combined. Two old men guard a large stone and admit to its hollow only Christians or those who desire to become Christians. If this profession of faith is genuine, the water in the hollow which is usually only four fingers deep thrice rises above the head of the person admitted, who thereupon emerges recovered from all sickness.[752] [Sidenote: The letter of Pope Alexander III.] How real Prester John was to the men of the twelfth century may be seen from the fact that Pope Alexander III on September 27, 1177, addressed from the Rialto in Venice a letter to him or to some actual eastern potentate whom he had confused with him.[753] The Pope does not expressly mention Prester John’s letter to Manuel but says that he has heard of him from many persons and common report, and more especially from “Master Philip, our friend and physician,” who had talked “with great and honourable men of your kingdom,” by whom he had been informed of their ruler’s desire for a church and altar at Jerusalem. It is this Philip whom the Pope now sends with his letter to Prester John and to instruct him in the doctrine of the Roman church. But it is a long and laborious journey involving many hardships and vicissitudes and the traversing of many countries with barbarous and unknown languages. [Sidenote: Philip, the papal physician.]