As if Stonehenge wasn’t impressive enough, its rocks were quarried from a very, very long distance away. Now, researchers have zoomed in on the source of the rocks, identifying it at an outcrop in Wales, 180 miles away from the site.

The Welsh quarry where the rocks were brought from. Image credits: UCL.

Stonehenge, which lies firmly in England, used rocks quarried from Wales. Geologists have long known that at least 42 of Stonehenge’s smaller stones, known as ‘bluestones’, came from the Preseli hills in Pembrokeshire, west Wales. The new study shows exactly where these rocks were quarried from.

“This was the dominant source of Stonehenge’s spotted dolerite, so-called because it has white spots in the igneous blue rock. At least five of Stonehenge’s bluestones, and probably more, came from Carn Goedog,” said geologist Dr. Richard Bevins from the National Museum of Wales.

This is rather unusual, as most megaliths of the time are built with rocks from no more than 10 miles away — which is very reasonable, considering how difficult it would have been to carry these big rocks over miles and miles. Especially in Europe, Neolithic megaliths were built with local rocks, says Professor Mike Pearson. Scientists have been trying to understand what makes Stonehenge such a remarkable outlier.

“We’re now looking to find out just what was so special about the Preseli hills 5,000 years ago, and whether there were any important stone circles here, built before the bluestones were moved to Stonehenge.”

According to the study, the bluestone outcrops consist of natural, vertical pillars. It wouldn’t have been all that difficult to extract from the outcrop, particularly compared to the stone quarries in ancient Egypt, which often consisted of much more solid rocks like basalt or granite. The tools they had, however, were woefully unfit for this type of job.

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The Stonehenge workers actually left some traces of their work behind. Archaeologists have discovered tools such as hammer stones and stone wedges, but these wedges were much softer than the rocks.

“The stone wedges are made of imported mudstone, much softer than the hard dolerite pillars. An engineering colleague has suggested that hammering in a hard wedge could have created stress fractures, causing the thin pillars to crack. Using a soft wedge means that, if anything were to break, it would be the wedge and not the pillar,” said Professor Parker Pearson.

Transportation, however, would have been even more difficult. Excavations around the outcrop have uncovered the remains of man-made platforms of stone and Earth. Archaeologists also suspect that the builders used perishable ropes and levers.

“Bluestone pillars could be eased down onto this platform, which acted as a loading bay for lowering them onto wooden sledges before dragging them away,” said Professor Colin Richards (University of the Highlands and Islands), who has excavated Britain’s only other identified megalith quarry in the Orkney islands, off the north coast of Scotland.

The new discovery also works against a popular theory, which claimed that the rocks were carried on water, using rafts.

“Some people think that the bluestones were taken southwards to Milford Haven and placed on rafts or slung between boats and then paddled up the Bristol Channel and along the Bristol Avon towards Salisbury Plain. But these quarries are on the north side of the Preseli hills so the megaliths could have simply gone overland all the way to Salisbury Plain,” said Professor Kate Welham (Bournemouth University).

So some of the Stonehenge rocks were quarried with soft tools and carried using rudimentary platforms over 180 miles, an absolutely grueling journey — and we’re really not sure why.

The team now believes that Stonehenge was initially a circle of rough, unworked bluestones set in shallow pits (called the Aubrey holes). Over time, more rocks were added, finessed, and re-arranged.

The findings have been published in the journal Antiquity.