WASHINGTON: Stonehenge, a Neolithic wonder in southern England, has vexed historians and archaeologists for centuries with its many mysteries: How was it built? What purpose did it serve? Where did its towering sandstone boulders come from? The answer to the last question may finally have an answer after a study published on Wednesday found that most of the giant stones — known as sarsens — seem to share a common origin 25 kilometres away in West Woods, an area that teemed with prehistoric activity.

The finding boosts the theory that the megaliths were brought to Stonehenge about the same time: around 2,500 BCE, the monument’s second phase of construction, which in turn could be a sign its builders were from a highly organised society.

It also contradicts a previous suggestion that one large sarsen, the Heel Stone, came from the immediate vicinity of the site and was erected before the others. The new paper appeared in the journal Science Advances.

Lead author David Nash, a professor of physical geography at the University of Brighton, said the technology required to analyse the sarsens, that stand up to nine metres tall and weigh as much as 30 metric tons, did not exist until recently.

He and his team first used portable x-rays to analyse the chemical composition of the rocks, which are 99 percent silica but contain traces of several other elements.

“That showed us that most of the stones have a common chemistry, which led us to identify that we’re looking for one main source here,” said Nash.

Next, they examined two core samples from one of the stones that were obtained during restoration work in 1958 but which then went missing until resurfacing in 2018 and 2019, respectively.

They performed a more sophisticated analysis technique called mass spectrometry on these samples, which detects a bigger range of elements at a higher precision.

The resulting signature was then compared to 20 possible source sites for these sedimentary rocks, with West Woods, Wiltshire found to be the closest match.

Previous work has found that Stonehenge’s smaller “bluestones” came from Wales, about 200 kilometres to the west, and the new study says that they and the sarsens were placed at the same time.

“So it must have been an enormous endeavor going on at that time,” said Nash. “Stonehenge is like a convergence of materials being brought in from different places.” Just how the early Britons were able to transport the boulders weighing up to 30 tons a distance of 25 kilometres remains unknown — though the prevailing idea is they were dragged along sleds. The site’s significance also remains mysterious. “I think you’re looking at a very organized society there,” added Nash.

As for why they picked West Woods, he said, it could have been a case of pragmatism as it was one of the closest sites.

Published in Dawn, July 30th, 2020