Researchers in the United Kingdom have finally solved a major piece of Stonehenge’s enduring mystery: the place of origin for some of the ancient structure’s most-famous rock formations.

The National Museum Wales and Leicester University have identified the source as Craig Rhos-y-felin, located more than 100 miles from the Stonehenge site. But this discovery, of course, just opens on to another mystery—namely, just how and why an ancient culture carved and transported the giant stones over such a great distance.

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Over the past nine months, the researchers compared mineral content and textural relationships of the rhyolite debitage stones found at Stonehenge and were finally able to pinpoint the location to within several meters of their source. Ninety-nine percent of the samples could be matched to the rocks found at Craig Rhos-y-felin, which differ from all others found in south Wales.

Further research should help the researchers eventually understand how the rocks made the long journey to Stonehenge sometime between 3000 and 1600 BC. “Many have asked the question over the years, how the stones got from Pembrokeshire to Stonehenge,” said Dr. Richard Bevins, National Museum Wales. “Thanks to geological research, we now have a specific source for the rhyolite stones from which to work and an opportunity for archaeologists to answer the question that has been widely debated.”