provided that they've not been covered up by blowing soil. noid bower found a total of forty circular ditches. in the vine fearful region of northeastern austria. in two thousand and five archaeologist. there and his team reconstructed one of these ditches near the town of helton bag they used stone tools and the same materials that would have been available during the stone age including wood bone and plant fibers. but it's the stone structures that tell us the most about our ancient ancestors. on the north sea island of silt for example there are more than five hundred burial sites made of stone.