The origins of Stonehenge’s massive stone monoliths, long shrouded in mystery, have at last been demystified. Experts have traced them to boulders in the nearby chalk hills of Marlborough Downs, just 15 miles north of the prehistoric monument in Wiltshire, England.
The discovery, published this week by researchers from the University of Brighton in the journal , actually confirms long-held theories that the sandstone slabs, called sarsens, were from somewhere in Marlborough Downs, but uses scientific testing to pinpoint the exact location to the West Woods for the first time.
“Until recently, we did not know it was possible to provenance a stone like sarsen,” David Nash, a geomorphologist and the lead author of the study, in a statement. “It has been really exciting to use 21st century science to understand the Neolithic past and answer a question that archaeologists have been debating for centuries.”
Nash believes the ancient builders transported the stones, which weigh up to 30 tons, down the Wiltshire Avon Valley to the east or via a western route across Salisbury Plain. “We can feel the pain of the Neolithic people who took part in this collective effort and think about how they managed such a Herculean task,” wrote Nash and his coauthor, Timothy Darvill, a Bournemouth University archaeology professor, in the Conversation.
Stonehenge actually contains two different kinds of stones, erected thousands of years apart. The sarsens are the larger silica stones in Stonehenge’s outer ring and center, each about 13 feet high and seven feet wide. There 52 on the site today, but experts believe that there were originally 80.
The other smaller stones within the inner circle are known as bluestones, erected around 3,000 BC. In 2015, experts found evidence that those stones came from the Preseli Hills, 180 miles away in western Wales. The exact sites, Carn Goedog and Craig Rhos-y-felin, were identified in 2019, after eight years of research. But investigations into the sarcens, erected around 2,500 BC, had lagged.
The new research was made possible thanks to a former diamond cutter, Robert Phillips, who was involved in repairs carried out on the prehistoric structure in 1958. To re-erect a fallen trilithon, one of the three-piece standing stones, Phillips and his team drilled holes and inserted metal bolts to reinforce the cracked lintel stone.
Phillips kept one of the three-and-a-half foot cylindrical cores, which was set to be discarded, as a souvenir, hanging it in his office. Sixty years later, Phillips, on the eve of his 90th birthday, returned the core to English Heritage, which oversees Stonehenge.
Immediately, archaeologists realized that this was a rare opportunity to investigate the landmark’s origins—drilling the stones at Stonehenge today is prohibited. “It’s the sarsens’ time, really,” Robert Ixer, a geologist at the University College London Institute of Archaeology, told magazine. “They have been for too long neglected.”
Unlike the stones on site, the core doesn’t have any surface weathering, which can affect readings of its chemical composition. More importantly, the team was allowed to use destructive sampling, pulverizing about half the sample for a thorough chemical analysis. Then, they used a portable x-ray spectrometer to take non-invasive surface readings of all 52 stones on site.
All but two shared a near-identical chemical makeup with the core sample, suggesting a common origin. The stones are 99 percent silica, with traces of aluminum, carbon, iron, potassium, and magnesium.
Comparing the chemical signature to mass spectroscopy readings on samples from 20 boulder fields across southern and eastern England, the researchers identified the West Woods as a match with nearly 100 percent certainty.
“We weren’t really setting out to find the source of Stonehenge,” Nash told the . “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 discovery narrows the point of origin from the 75-square-mile Marlborough Downs to just two square miles in the West Woods.
Even with this long-awaited find, however, Stonehenge still holds plenty of secrets. Experts have yet to determine, for example, exactly how the builders chose where to get the stones. Plus, “we still don’t know where two of the 52 remaining sarsens at the monument came from,” Nash told NBC News. “There remain mysteries to solve.”