Thunderstones

One of the weirder objects sometimes found in medieval graves is a neolithic stone ax made thousands of years before the person in the grave was even born. Skeptics have sometimes said these were accidental inclusions, but a recent study shows there are so many such axes that their burial must have been intentional. The Vikings and the people of southern England and northern France were particularly fond of this rite. This is the same area within which the practice of placing a "thunder stone" in the roof of a house to ward off lightning is well documented for medieval and early modern times.

There is more. The association between stone tools and lightning is much older than these examples, which you can see by examining the worldwide distribution of the myth. American Indian myths that connect stone axes or knives with thunder, lightning, blood, magical dwarves, and divine twins are so similar to myths from Siberia that the whole complex must be at least 13,000 years old. The Norse myths have many connections with those of Siberia, so the Norse picture of Thor and his thunder hammer seems to be another expression of the underlying myth. People and our ancestors have been making stone tools for millions of years, and we maybe have been using prepared stones to make fire for nearly as long. The parallel between lightning and the striking of sparks with stones must have greatly impressed the first people who mastered this technology. The myth of the divine thunderer with his stone ax may be that old. So the thunder stones in these Viking graves may express a religious idea that goes back to Homo erectus or at least the Neanderthals.