In the ongoing effort to unlock the mysteries of Stonehenge, geologists have shifted their focus on the origins of the monument’s central Altar Stone. Recent findings have redirected the search from Wales to northeastern Scotland, offering fresh clues to the age-old question.
However, in a surprising twist, new research has ruled out Orkney, an island off Scotland’s northeastern coast, as the Altar Stone’s origin, despite the archipelago's rich Neolithic history.
Published in the Journal of Archaeological Science: Reports on September 5, the findings come just after an August study in Nature that pointed to northeastern Scotland as the most likely source. This overturned a century-long belief that the stone originated from modern-day Wales.
The Altar Stone, weighing about 13,227 pounds (6 metric tons), is the largest of the bluestones used at Stonehenge and lies at the heart of the ancient monument in southern England. Transported from Scotland nearly 5,000 years ago—possibly by sea—the true purpose of the stone remains a mystery.
A geological team, including many authors from the original Nature study, analyzed Neolithic stones from two historic sites on Orkney’s Mainland island. Despite the similarities in size and composition, no link between these stones and the Altar Stone was found.
“The mystery of the stone's origin is becoming clearer as we eliminate specific areas in northeast Scotland,” said Richard Bevins, honorary professor at Aberystwyth University, who led the research team. “Our chemical analysis and dating work are slowly unlocking this ancient mystery.”
Piecing Together the Puzzle
Construction on Stonehenge began as early as 3000 BC, evolving through several phases. The Altar Stone, believed to have been placed during the second phase between 2620 BC and 2480 BC, holds a prominent position within the central horseshoe formation.
Research over the years has focused on identifying the various stones used to build the monument. Earlier studies revealed that Stonehenge is primarily made up of two types of stones: sarsens, which are silicified sandstone blocks, and bluestones, a fine-grained sandstone. The sarsens were sourced from West Woods near Marlborough, around 15 miles from the site, while the bluestones were transported from the Preseli Hills in Wales.
Yet, as Professor Bevins explained, the Altar Stone stands apart. “It occupies an unusual near-central position in the monument and is not part of the Bluestone Circle or Horseshoe,” he said. “It is also made of grey-green sandstone, unlike other bluestone types.”
After 15 years of investigating Stonehenge, Bevins’ discovery that Wales is unlikely the origin of the Altar Stone marked a significant breakthrough. “Suddenly, new avenues of exploration were opened up,” he said.
A Shift in Focus: Investigating Scotland
In June 2023, researchers turned their attention to Scotland’s Mainland island, conducting fieldwork to explore potential connections between Stonehenge and Orkney. Previous archaeological findings suggested a long-standing link between the two locations, as seen in shared pottery styles and similar architectural structures from the Neolithic period.
The team used portable X-ray machines to analyze the mineral compositions of rocks at the Stones of Stenness and the Ring of Brodgar, two ancient stone circles on Mainland. Dating back more than 5,000 years, these monuments are among the earliest in the British Isles.
Despite initial hopes, the analysis revealed no mineralogical connection between the Altar Stone and these Orkney sites.
However, the search is far from over. The researchers now believe the Altar Stone likely originated elsewhere in northeastern Scotland. Potential areas for further investigation span from Orkney and Shetland down through Caithness, Sutherland, Inverness, and eastward to Aberdeenshire.
What’s Next?
Identifying the true source of the Altar Stone could provide critical insights into the Neolithic people who built Stonehenge and the technologies they used. “As an academic, Stonehenge has always fascinated me,” Bevins said. “I and my colleagues will continue working to determine exactly where in northeast Scotland the Altar Stone came from.”
Discovering the Altar Stone’s origin would not only deepen our understanding of Stonehenge but also shed light on the advanced skills of its builders, offering new perspectives on Britain’s ancient history.
