Actually a stonegrave from the Neolithic Age (3000 B.C.), the X-tians made the following story outta it:
The Devil was on his way to Aachen, where he wanted to destroy the dome of Charles the Great, for this he collected some stones to throw on the dome.
On his way, he met a shoemakers apprentice boy, who carried 12 pairs of town shoes.
The Devil asked the boy, how far it is to walk to the dome of Aachen.
The shoemaker apprentice realized, that he was talking to the Devil, he had seen his cloven hoof and replied:
OH, that's SO FAAAR away, that I have worn out these 12 pairs of shoes to get there!!
The Devil got furious, canceled the plan to destroy the dome of Aachen and threw his collected stones on the ground.
So, an ancient stonegrave became "The Devil's Stones".