But while different copies of the work vary, all have the same general character. Prester John tells what a mighty and Christian potentate he is and describes his marvelous palaces and contrivances or the natural marvels, strange beasts and serpents, monstrous races of men, potent herbs, stones, and fountains, to be found in the lands owning his sway. In one province is the herb _assidios_ which enables its bearer to rout an impure spirit and force him to disclose his name and whence he comes. “Wherefore impure spirits in that land dare not take possession of anyone.”[737] A fountain flows from Mount Olympus not three days’ journey from Paradise whence Adam was expelled. Three draughts from it taken fasting insure one henceforth from all infirmity, and however long one may live, one will seem henceforth but thirty years of age.[738] Then there are some little stones which eagles often bring to Prester John’s territories and which worn on the finger preserve or restore the sight, or if consecrated with a lawful incantation, make one invisible and dispel envy and hatred and promote concord.[739] After a description of a sea of sand in which there are various kinds of edible fish and a river of stones, Prester John soon mentions the worms which in his language are called salamanders, who cannot live except in fire, and from whose skins he has robes made which can be cleansed only by fire.[740] After some boasting concerning the absence of poverty, crime, and falsehood in his country and about the pomp and wealth with which he goes forth to war, Prester John then comes to the description of his palace, which is similar to that which the Apostle Thomas built for Gundaphorus, King of India. Its gates of sardonyx mixed with _cornu cerastis_ (horn of the horned serpents) prevent the secret introduction of poison; a couch of sapphire keeps John chaste; the square before the palace where judicial duels are held is paved with onyx “in order that the courage of the fighters may be increased by the virtue of the stone.”[741] Near this square is a magic mirror which reveals all plots in the provinces subject to Prester John or in adjacent lands.[742] In some manuscripts of the twelfth century is a description of another palace which before Prester John’s birth his father was instructed in a dream to build for his son. One feature of it is that no matter how hungry one may be on entering it, he always comes out feeling as full as if he had partaken of a sumptuous banquet.[743] [Sidenote: Additional marvels in later versions.]