Pierres de Axular y las cuevas de Salamanca

This fable dates back to the end of the reign of the Goths though it was changed little by little. In the caves of Salamanca there used to be a demon who used to teach magic arts. It only admitted seven pupils on the condition of keeping one of them in body and soul, but he was foiled. In the Basque Country it was widely believed that Axular was the one who had foiled the demon