Researchers aren't sure what the purpose of the Altar Stone at the center of Stonehenge was, but they now know where it came from—and it traveled a lot farther than they expected. According to a study published in the journal Nature, the six-ton sandstone slab came from Orcadian Basin formations in northeast Scotland, meaning it traveled at least 460 miles. Researchers say it would have been almost impossible for glaciers to have brought it to southern England, meaning it was most likely transported to the site by sea or by land around 4,500 years ago, before spoked wheels were invented, NBC News reports.
The researchers say that since transporting the 16-foot slab over land would have meant crossing many rivers and heavily forested areas, it was most likely carried by boat on a journey of more than 600 miles around Britain's shoreline. The fact that it made it to the site at all "tells us an awful lot about Neolithic society and its connectivity," says study co-author Chris Kirkland. The Altar Stone, which lies flat in the middle of Stonehenge, traveled much farther than other stones at the site, some of which came from Wales, more than 100 miles away from the site in southwest England.
- 'Miniature atomic clocks': Study co-author Anthony Clarke says researchers analyzed grains of zircon, apatite, and rutile from the stone, the New York Times reports. "All three minerals contained uranium, which effectively made them miniature atomic clocks," Clarke says. He says that when the ages of the minerals were "squished" together to create a "fingerprint" of the stone's origin, it "revealed a striking similarity to the sandstone of the Orcadian Basin."
- The Orkney Islands connection: The Orcadian Basin includes the Orkney Islands, off the northern tip of Scotland. Previous research has found cultural connections, including similar pottery styles, between Neolithic peoples in the Orkneys and the Stonehenge region, the AP reports.
- A 'special stone': Stonehenge was built to align with the sun at the winter and summer solstices, but it's not clear what role the Altar Stone played. "It's a special stone for whatever reason," says Stonehenge expert David Nash at the University of Brighton, per NBC. "It's a very different stone to all of the other stones at the monument."
- What the legends say: The Times notes that according to legends from the time of King Arthur, the wizard Merlin brought stones including the Altar Stone from Ireland to Stonehenge. The legends claim that Merlin, with the help of an army raised by the king's brother, took the stones from Mount Killaraus, where they "had been erected by giants who used them for their magical and medicinal properties," per UCL Press.
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