A Stonehenge secret revealed.

A team of archaeologists in the United Kingdom says it has traced dozens of Stonehenge’s massive rocks to two quarries in west Wales. The rocks were transported 180 miles — dragged on wooden sleds, the scientists suggest, by teams of strong men. These stones, called bluestones after their bluish-gray hue, form the inner circle of the monument that towers over the Salisbury Plain.

Two bluestone quarries, named Carn Goedog and Craig Rhos-y-felin, were excavated around 3000 B.C., according to the authors of a study published this week in the journal Antiquity.

Expeditions at the quarries from 2014 to 2016 recovered ancient charcoal and stone tools. In some places, the charcoal was mixed with dirt and stones to form flat platforms, which may have been used like loading bays to distribute the massive pillars, said Michael Parker Pearson, an archaeologist at University College London and an author of the new study.

Among the Welsh hills, bluestones erupted from the ground. Here, millions of years ago, sheets of magma slowly cooled into columns. Eons passed and softer rock around the magma eroded. Only the jagged bluestones remained.

Prehistoric workers probably exploited natural weaknesses in these structures, Parker Pearson said. “They’re nearly vertical,” he said. “All you’ve got to do is get a lasso around each one and pull.”

With ropes and simple tools, such as sandstone wedges shoved into the outcrop’s joints, excavators may have plucked out a pillar as cleanly as a loose tooth. Those on top of the outcrop could have carefully slackened their ropes to control the pillar’s descent to a platform below, the authors wrote.

From there, workers may have lowered a stone, 6 feet long and weighing two to four tons, onto a wooden sled to haul it away.

Bluestones are big, but not so big that a “burly group of Stone Age men” couldn’t drag them across the countryside, Pearce said.

These pillars are “the Ikea version of Neolithic megaliths,” Parker Pearson joked — the stones peeled off the outcrop as though from ready-to-use kits. Unlike the people who crafted Egypt’s obelisks from much larger rocks, Stonehenge’s builders did not need to rework the bluestone pillars.

The bluestones, which are speckled with fingernail-size deposits of white minerals, form an inner horseshoe and ring at Stonehenge. These rocks, though impressive, are not Stonehenge’s biggest. The imposing sandstone trilithons, the three-part structures made of two vertical stones and a horizontal top, are larger and more locally sourced, though their exact origins are unknown.