Geologists may have solved the mystery of the origin of the Altar Stone central to the ancient monument of Stonehenge on the Salisbury Plain in Wiltshire, England.

The Altar Stone was long believed to have traveled 150 miles from Preseli Hills in Southwest Wales with the other megaliths until later work discounted that theory.

According to new research published in the scientific journal Nature, the 6-ton Altar Stone may have taken a longer journey of 600 miles from Northern Scotland.

“The difficulty of long-distance overland transport of such massive cargo from Scotland, navigating topographic barriers, suggests that it was transported by sea,” the study said. “Such routing demonstrates a high level of societal organization with intra-Britain transport during the Neolithic period.”

According to the study, ancient Britons began construction of Stonehenge as early as 3000 B.C. and continued for two millennia.

Stonehenge was constructed with sarsen stones and bluestones—or rock “considered exotic to the local area,” the study said.

The Altar Stone, the study said, is the largest of the bluestones in the ancient monument.

Stonehenge’s Origin

Nick Howe, host of Nature’s “Nature Podcast,” said the Altar Stone has long perplexed geologists.

“Despite its name, it’s unclear whether it was actually used as an altar,” he said. “And while it now lies flat, with another stone fallen on top of it, it may have once stood upright.”

Because it’s the largest of the stones and central to the structure, researchers have acknowledged its importance, Mr. Howe said.

Ten thousand years ago, he said, Stonehenge was marked not with stones but with wooden posts, which suggested that the site had significance for the ancient Britons.

“Then, around 6,000 years ago, a round ditch was constructed, the first signs of the familiar circular structure,” he said. “It’s around this time that it’s thought that a set of stones, known as the bluestones, arrived at Stonehenge from the Preseli Hills in Wales, a journey of some 150 miles.”

Hundreds of years later, the over 20-foot sarsen stones were transported to the site and raised to create what is known as Stonehenge today.

“It’s thought that these massive slabs came from quite close by, maybe only 15 miles away,” Mr. Howe said.

Despite competing theories suggesting the Altar Stone arrived with either the sarsen or the bluestones, researchers have never reached a definitive conclusion, Mr. Howe said.

“Last year a detailed analysis ruled out a Welsh origin for the Altar Stone, so, until now, its origin has remained a mystery,” Mr. Howe said.

‘Unique Fingerprint’

The study’s co-author, geologist Richard Bevins at Aberystwyth University in Aberystwyth, Wales, wasn’t allowed to use samples from the Altar Stone because it’s a protected site.

Instead, he used a sample from the rock in the 19th century and sent it to Anthony Clarke, a PhD student at Curtin University in Perth, Western Australia, where he had the technology to analyze the sample “grain-by-grain.”

“From that chemistry, we could look up the ages and compare them with other source regions in the UK,” he said.

Using this analysis, he then set about finding a match for the source of the Altar Stone.

Though it’s a small island, Britain has a complicated geology, Mr. Clarke said.

Mr. Clarke was able to determine the “unique fingerprint” of the Altar Stone and compare it with other sedimentary basins, eventually finding a match in the Arcadian Basin of Northeast Scotland.

Mr. Clarke told Mr. Howe that he intends to conduct further research to find the exact location of Northeast Scotland where the Altar Stone was taken, information which may help illustrate a relationship between the two distant regions.

“One thing is for sure, though,” Mr. Howe said. “This won’t be the end of the mysteries that Stonehenge holds.”