In the middle ages conjuration was regularly practised in Europe, and devils were supposed to appear under decided forms. A devil would appear either as an angel of light, or as a monster in hideous shape. An anonymous writer, discussing the subject, says: "A devil would appear either like an angel seated in a fiery chariot, or riding on an infernal dragon, and carrying in his right hand a viper, or assuming a lion's head, a goose's feet, and a hare's tail, or putting on a raven's head, and mounted on a strong wolf. Other forms made use of by demons were those of fierce warriors, or old men riding upon crocodiles, with hooks in hand. A human figure would arise, having the wings of a griffin; or sporting three heads, one of them being like that of a toad, the other resembling that of a cat; or defended with huge teeth and horns, and adorned with a sword; or displaying a dog's teeth, and a large raven's head; or mounted upon a pale horse, and exhibiting a serpent's tail; or gloriously crowned, and riding upon a dromedary; or presenting the face of a lion; or bestriding a bear, and grasping a viper. There were also such shapes as those of archers or bowmen. A demoniacal king would ride on a pale horse, assume a leopard's face and griffin's wings; or put on three heads, one of a bull, another of a man, and a third of a ram, with a serpent's tail and the feet of a goose; and in this appearance sit on a dragon, and bear in his hand a lance and flag; or, instead of being thus employed, goad the flanks of a furious bear, and carry on his fist a hawk. Other forms were those of a goodly knight; or of one who bore lance, ensign, and even sceptre; or of a soldier, either riding on a black horse, and surrounded with a flame of fire; or wearing on his head a duke's crown, and mounted on a crocodile; or assuming a lion's face, and, with fiery eyes, spurring on a gigantic charger, or, with the same frightful aspect, appearing in all the pomp of family distinction, on a pale horse; or clad from head to foot in crimson raiment, wearing on his bold front a crown, and sallying forth on a red steed." To inferior demons was assigned the duty of carrying away condemned souls, and superior benign spirits had the pleasing task of conveying from earth the souls of the blessed. Toledo, Seville, and Salamanca were great schools of magic. The teachers taught that all knowledge might be obtained by the assistance of fallen angels. These teachers were skilled in the abstract sciences, in alchemy, in the various languages of mankind, and of the lower animals, divinity, magic, and prophecy. They professed to possess the power of controlling the winds and waters, and of influencing the stars. They also pretended to be able to cause earthquakes, spread diseases or cure them, release souls out of purgatory, to influence the passions of the mind, procure the reconciliation of friends or foes, engender discord, and induce mania and melancholy.