According to a popular story, he was accosted on his journey by a courteous stranger who promised to teach the art of magic at Toledo.

As payment, so the legend runs, the stranger required that Giles should make over his soul to the devil and sign the compact with his blood.

Giles obeyed and after devoting himself seven years to the study of magic under the direction of Satan, went to Paris, easily obtained the degree of doctor of medicine, and performed many wonderful cures.

One night while he was locked up in his library a gigantic knight, armed head to foot, appeared to him and, with his sword drawn, demanded that Giles should change his wicked life.

Here he led a life of prayer and penance, and for seven years his mind was tormented by the thought of the compact which was still in the hands of Satan.