Back in the 30s — the 1130s — the Welsh cleric Geoffrey of Monmouth created the impression that Stonehenge was built as a memorial to a bunch of British nobles slain by the Saxons. In his “Historia Regum Britanniae,” Geoffrey tells us that Merlin, the wizard of Arthurian legend, was enlisted to move a ring of giant mystical stones from Mount Killaraus in Ireland to what is commonly believed to be Salisbury Plain, a chalk plateau in southern England, where Stonehenge is located.
Back in the 50s — the 1950s — a chunk of rock went missing from the magical tumble of megaliths that now comprise Stonehenge. The chunk, a three-and-a-half foot cylindrical core, had been drilled out of one of the site’s massive sarsen stones during repairs and taken home by an employee of the diamond-cutting firm that carried out the work.
The core, recently repatriated after 60 years, turned out to be pivotal to an academic paper published on Wednesday in the journal Science Advances. The study pinpointed the source of the sarsens, a mystery that has long bedeviled geologists and archaeologists.
Although the project did not identify the specific spot where the stones came from, Mike Pitts, editor of the magazine British Archaeology, believes that the discovery makes the search for sarsen quarries a realistic option. “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 said. “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.”
Two kinds of stones make up the roughly 5,000-year-old monument known as Stonehenge. A small inner horseshoe consists of 2- to 4-ton blocks of varied geology, called bluestone after the bluish-gray hue they have when wet or freshly broken. The sarsens, sandstone slabs that weigh 20 tons on average, form Stonehenge’s enormous central horseshoe, the uprights and lintels of the ragged outer circle, as well as the outlying Heel Stone, Slaughter Stone and Station Stones.
Geologists determined nearly a century ago that the bluestones were dragged, carried or rolled to Stonehenge from somewhere in the Preseli Hills in western Wales, some 180 miles away. Last year a team of archaeologists led by Michael Parker Pearson of University College London revealed evidence of the exact location of two of the quarries.
As for the sarsens, conventional wisdom holds that they derived from deposits on the highest points of the Marlborough Downs, 18 miles north of Stonehenge.
David Nash, a geomorphologist at the University of Brighton and lead author on the new sarsen study, said the idea that the slabs hailed from the Downs dates to the writings of William Lambarde, a 16th-century antiquarian.
“Lambarde came to that conclusion based on little more than the appearance of the stones on the Downs and their similarity to those at Stonehenge,” Dr. Nash said. “This idea has stuck around for more than 400 years but has never been tested.”
Dr. Nash has traced the source of almost all the sarsens to West Woods, on the southern edge of the Downs and several miles closer to Stonehenge. His team analyzed the geochemical fingerprint of the 52 sarsens that remain in situ at the ancient site.
The breakthrough came last summer when the long-lost core from Stone 58 was returned to English Heritage, the charity that manages Stonehenge. The sarsen cylinder offered Dr. Nash the unique opportunity to analyze a sample unaffected by surface weathering, which can slightly alter the chemical composition. Drilling through the ancient stones is now discouraged.
“There are literally thousands of pieces of sarsen sitting in museums across Britain,” he said. “However, to my knowledge, the core from 58 is the only piece where we can identify precisely which stone it came from.”
To determine its chemical makeup, researchers used a variety of noninvasive spectrometry techniques. Once the geochemical signature was established, they sampled sarsens from 20 locations across southern England, including six on the Downs. A data set comparison resulted in a single match, West Woods.
Only two of the sarsens, Stones 26 and 160, appear to have come from elsewhere in the region. “The biggest surprise for me was finding out that the chemistry of the remaining sarsens was so consistent,” said Dr. Nash. “I expected a little more variability.”
The only other authority thought to have linked West Woods and Stonehenge is John Aubrey, biographer and philosopher who surveyed the monument in the 17th century and was the first to record a ring of 56 chalk pits, now called Aubrey Holes. “Aubrey reckoned that he’d found the source of Stonehenge’s sarsens, a large quarry pit just 14 miles north of Stonehenge,” said Dr. Parker Pearson. “Given that West Woods is around 15 miles away, it’s very possible that he got it right the first time! And it’s taken us 340 years to find out again.”
For his part, Dr. Nash writes it off to archaeologists “not seeing the wood for the trees.”
Or perhaps leaving stones unturned.
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