The people who built Stonehenge are renowned for hauling the megalithic bluestones 225km from the Preseli Mountains in Wales to their final home on Salisbury Plain.

But, perhaps that mammoth journey proved too much for them to maintain because when it came to sourcing the larger sarsen stones later on they looked far closer to home.

Archaeologists from English Heritage and the University of Sheffield have finally solved a centuries-old mystery and concluded that the sarsens originated in the West Woods of the Marlborough Downs, just 24km north of Stonehenge and not far from the Neolithic monument site at Avebury.

The breakthrough came when a core - drilled from Stonehenge's "Stone 58" during repair work in the Fifties - was returned to English Heritage from the US last year.

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It finally gave archaeologists the chance to analyse the chemical make-up without damaging the monument.

Historian Susan Greaney said: "The bluestones, we've known, come from mid-west Wales and they were easy to source because there are inclusions and quartz which you can match to the outcrop. The large stones are pretty uniform and just look like a big block, so it's difficult to interrogate them and find where they are from."

Researchers used X-ray spectrometry to look at the very small trace elements and it was found the Stonehenge sarsens matched those in the Marlborough Downs. The Stonehenge sarsens weigh about 20 tonnes but some are as heavy as 30 tonnes and the largest is 9m long.

"There are no sarsens of this size left in the downs, that's why it's been such a mystery and some people have suggested they come from elsewhere as you get outcrops in other places where you have chalk land, like Devon and Kent," Greaney added.


"The west wood was overlooked because it's under ancient woodland and a lot of sarsens were removed in the 19th century for road stones, particularly in Swindon, but there are still sarsens buried in among the trees. To be able to pinpoint the area that Stonehenge's builders used to source their materials around 2500 BC is a real thrill."

While the Preseli stones were probably chosen for ritualistic reasons, the sarsens were most likely picked for their size, archaeologists believe.

But although 10 times shorter than the journey from Wales, moving 30-tonne stones would still have proven a tricky prospect and the sarsens may have travelled on the River Avon for part of the way.

"We can now say, when sourcing the sarsens, the overriding objective was size - they wanted the biggest, most substantial stones they could find and it made sense to get them from as nearby as possible," said Greaney.

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"This is in stark contrast to the source of the bluestones, where something quite different - a sacred connection to these mountains perhaps - was at play.

"Yet again this evidence highlights just how carefully considered and deliberate the building of this phase of Stonehenge was."

Professor David Nash from the University of Brighton, said: "It has been really exciting to harness 21st-century science to understand the Neolithic past, and finally answer a question that archaeologists have been debating for centuries."

The team is now hoping to carry out more work on the Marlborough Downs looking for sarsen chips and wedges which could pinpoint the original location of the stones.

The research was published in the journal Science Advances.