At a Glance

Two quarries in Wales, 180 miles from Stonehenge, appear to be the source of the monument's bluestones.Archaeologists think ancient stonemasons used wedges to crack the pillars free from their neighbors.The pillars could have been hauled to southern England on wooden sleds.

Archaeologists in the United Kingdom say they have located two ancient quarries that were the source for the bluestones at Stonehenge.

The bluestones were the smaller standing stones used to create an inner horseshoe shape and an outer ring at the giant stone monument in southern England.

The bigger stones stacked on the outer ring of Stonehenge, the trilithons, are composed of sandstone and were quarried much closer to the monument.

Scientists have known for a long time that the bluestones, named for their bluish-gray hue, came from the Preseli Hills of western Wales.

(MORE: China Closes Mount Everest Base Camp to Tourists to Battle Trash)

The latest research reveals the exact geological sources of some of the stones and , according to a study published this week in the journal Antiquity.

Excavations found evidence that prehistoric humans used mudstone and sandstone wedges and stone hammers more than 5,000 years ago to pry the giant stones from two quarries, Carn Goedog and Craig Rhos-y-felin, in far western Wales.

The rocky outcrops in those two areas are made of lava from volcanic eruptions. As the lava cooled, it , Ars Technica writes.

Some of the pillars of bluestone at Carn Goedog in western Wales are up to 12 feet tall.

(Adam Stanford/University College London)

The ancient stonemasons could drive the wedges into the cracks and break the pillars free from its neighbors.

“,” Michael Parker Pearson, an archaeologist at University College London and an author of the new study, told the Washington Post. “All you’ve got to do is get a lasso around each one and pull.”

The archaeologists also found platforms at the base of the rocky outcrops that may have been used like loading docks are used today.

The stonecutters could have used ropes to lower the pillars onto logs arranged on the platforms. The pillars could then be rolled onto wooden sleds and hauled away (coincidentally, in 3000 BC, as these stones were being quarried in Wales, stonecutters in Egypt were cutting giant stone slabs for the pyramids).

It had to be a long, hard trip. The bluestone megaliths weighed 2 to 4 tons each, and the Stonehenge site was 180 miles from the quarries.

(MORE: Australia's Great Barrier Reef Inundated by Queensland Flood Plumes)

One of the big questions that remains is what was the connection that brought Stone Age humans from western Wales to southern England.

A study last year foundat Stonehenge that suggested the people could have come from areas near the bluestone quarries.

"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," Pearson told Ars Technica.