For some 60 years, Englishman Robert Phillips displayed an illicit souvenir in his office and later his home. From time to time, he gazed at the broomstick-sized cylinder of polished rock, perhaps with a twinkle in his eye at the thought of its backstory. Then, on the eve of his 90th birthday in 2018, the British expatriate decided to send the three-and-a-half-foot chunk of rock back to its original home: Stonehenge.
Geochemical analyses published this week in the journal Science Advances have determined that 50 of the 52 sarsen megaliths in the English heritage site’s outer ring originated in the West Woods of Wiltshire—a full 15 miles away.
As Franz Lidz reports for the New York Times, investigations conducted around 100 years ago previously determined that the smaller “bluestones” at Stonehenge’s center were sourced from somewhere in the Preseli Hills of western Wales, roughly 180 miles from the ancient monument.
To glean the larger stones’ provenance, researchers used a technique called X-ray fluorescence to test the sarsens’ chemical composition, according to BBC News.
Next, the team conducted more destructive tests on Phillips’ core to break down the rock’s components and create a clear geochemical “fingerprint” for the Stonehenge sarsens. Such decisive tests would have been impossible without the repatriated object.
Per the Guardian, the scientists—building off the knowledge that the 20-ton boulders share a similar composition and therefore probably came from the same location—then tested 20 spots across southern England known to feature similar sandstone. These assessments finally identified West Woods as the Neolithic monument’s rocky progenitor.
“We weren’t really setting out to find the source of Stonehenge,” lead author David Nash, a geomorphologist at the University of Brighton, tells the Guardian. “We picked 20 areas and our goal was to try to eliminate them, to find ones that didn’t match. We didn’t think we’d get a direct match. It was a real ‘Oh my goodness’ moment.”
The new research doesn’t pinpoint the exact spot the stones originated, but Mike Pitts, editor of British Archaeology magazine, tells the Times that homing in on the quarry where the megaliths were hewn is within the realm of possibility.
“If we can find them, we could learn about how they were dressed and moved, and importantly we might be able to date that activity,” he says. “Dating matters, because then we can say what else was present in the landscape at the same time, what was old or gone and what was still to come—other sites are better dated—and of course who actually built the thing.”
Nash tells Reuters’ Will Dunham that the mystery of how Stonehenge’s ancient builders moved the immense rocks to where they now stand remains unresolved.
“Given the size of the stones, they must have either been dragged or moved on rollers to Stonehenge,” he explains. “We don’t know the exact route but at least we now have a starting point and an endpoint.”