Feb. 19 (UPI) -- Scientists have traced the origin of Stonehenge's bluestones to a pair of 5,000-year-old quarries in Wales.
"What's really exciting about these discoveries is that they take us a step closer to unlocking Stonehenge's greatest mystery -- why its stones came from so far away," Mike Parker Pearson, professor of archaeology at the University College London, said in a news release. "Every other Neolithic monument in Europe was built of megaliths brought from no more than 10 miles away."
Bluestones are the smaller stones found at Stonehenge. Researchers traced the bluestones to two quarries in the Preseli Hills in West Wales. The largest of the two quarries is located on an outcropping called Carn Goedog, located 180 miles from Stonehenge.
"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 Richard Bevins, a geologist with the National Museum of Wales.
The rhyolite bluestones found at Stonehenge were traced to another quarry located on an outcropping called Craig Rhos-y-felin, located in a valley not far from Carn Goedog.
Both of the exposed igneous rock deposits made for excellent quarry sites due to their natural, vertical pillars. Unlike ancient Egyptian quarries, where large obelisks had to be carved from uniform stone, Neolithic quarries in Wales had only to insert a wedge into the joint separating the pillars, breaking off large readymade stone columns.
Archaeologists found stone hammers and wedges at the two quarry sites.
"The stone wedges are made of imported mudstone, much softer than the hard dolerite pillars," Parker Pearson said. "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."
Researchers also found the remains of human-made platforms where the stones were likely lowered before being loaded onto wooden sledges. The excavations revealed charcoal on the platforms dating to 3,000 BC, suggesting quarrying at the two sites began as early as 5,000 years ago.
The new findings -- published this week in the journal Antiquity -- undermine the theory that Stonehenge's bluestones were transported by sea.
"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," said Kate Welham, an archaeology professor at Bournemouth University. "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."