(CNN) Five thousand years after Stonehenge was built, archaeologists have finally pinpointed exactly where the bluestones that form part of the imposing UK monument came from and how they were unearthed.
The researchers revealed in 2019 the stones came from an ancient quarry on the north side of the Preseli Hills in western Wales, which meant the 43 huge bluestones had been moved a staggering distance of 150 miles.
Now, archaeologists have said they think some of the bluestones first formed another stone circle close to the same area as the quarries and were dismantled and rebuilt as part of Stonehenge on the Salisbury Plain.
The identical 110-meter diameters of the stone circle, known as Waun Mawn, and the enclosing ditch of Stonehenge, suggest that at least part of the circle was brought from its location in Wales to Salisbury Plain, according to new research published in the journal Antiquity.
What's more, both stone circles are aligned on the midsummer solstice sunrise, and one of the bluestones at Stonehenge has an unusual cross-section that matches one of the holes left at Waun Mawn, the paper said.
Chippings in that hole are of the same rock type as the Stonehenge stone, it added.
Stonehenge is made of two types of stone: larger sarsen stones and smaller bluestone monoliths.
Some 43 bluestones survive today at Stonehenge, though many of these remain buried beneath the grass.
They were thought to have been the first to be erected at Stonehenge 5,000 years ago, centuries before the larger sarsen stones were brought over just 15 miles from the monument.
The Stones of Stonehenge research project is led by Mike Parker Pearson, a professor at University College London.
Discovering the dismantled stone circle at Waun Mawn happened through trial and error, the news statement said.
Only four stones were visible at the site. It was thought in 2010 that they were part of a stone circle, but initial geophysical studies were inconclusive and the team decided to focus their energies elsewhere.
A trial excavation at the site in 2017 found two empty stone holes, but ground radar surveys were still unsuccessful, leaving the team with no choice but to do it the old-fashioned way and dig.
Excavations in 2018 revealed empty stone holes, confirming that the four remaining stones were part of a former circle.
Dating of charcoal and sediments in the holes found the Waun Mawn stone circle was erected around 3400 BC, the study said.
The paper also suggested that the stones may have been moved as people migrated from that part of Wales, with the first people to be buried at Stonehenge thought likely to have once lived in this region.
"My guess is that Waun Mawn was not the only stone circle that contributed to Stonehenge," said Parker Pearson in a news statement.
"Maybe there are more in Preseli waiting to be found. Who knows? Someone will be lucky enough to find them."