A New Discovery Just Upended What We Know About Stonehenge's Mysterious Origin

A new discovery has upended the accepted backstory of a central feature of Stonhenge, raising more questions about the mysterious origin of this iconic Neolithic site, reports a new study. 

One of Stonehenge’s most important monoliths, known as the Altar Stone, likely came from a completely different region of Britain than was proposed 100 years ago, according to researchers. The Altar Stone, also known as stone 80, is the largest of the “bluestones” that form the inner circle of Stonehenge, a mysterious 5,000-year-old monument in Wiltshire, England, that served as a ritual site for millenia. Measuring 16-feet-long, the Altar Stone lies in a recumbent position on the ground, giving it the appearance of an altar, though its original purpose remains unknown.

For the past century, researchers have assumed that the Altar Stone came from the Old Red Sandstone basin in the Mynydd Preseli region of western Wales that is the source of Stonehenge’s other bluestones. This origin story can be traced to an influential study published in 1923 by the geologist Herbert Henry Thomas, who suggested the bluestones were hauled from Wales across 140 miles to the Stonehenge site. 

Now, a team led by Richard Bevins, a geologist at Aberystwyth University in Wales, have presented new evidence that the Altar Stone does not match the Welsh deposits, throwing the conventional provenance of the stone into doubt. To that end, Bevins and his colleagues “question whether the Altar Stone should not be ‘lumped’ with the Welsh bluestones,” a finding that has inspired them to broaden their “search for the Altar Stone source into northern Britain,” according to a new study published in the Journal of Archaeological Science.

“We started the study by examining rocks from the Old Red Sandstone outcrops that Thomas (in his seminal 1923 paper) had proposed for the possible source of the Altar Stone in west Wales,” Bevins told Motherboard in an email. “Thomas seemed to want all of the bluestones to come from a limited area, in and around the Mynydd Preseli.” 

“We quickly ruled these out and so worked away from those sites, across south Wales, the Welsh Borderlands, Somerset, and the West Midlands,” he added. “Failing to find any matches led us to reappraise our thinking.” 

Bevins and co-author Rob Ixer, an archaeologist at University College London, first started investigating the provenance of the Altar Stone in 2009 by examining samples held by the Salisbury Museum. This work snowballed into a comprehensive effort to constrain the mineralogy, petrology, and geochemistry of the Stonehenge bluestones using sophisticated analytical techniques, such as automated scanning electron microscopy (SEM-EDS), U-Pb zircon age determination, and preliminary portable X-ray fluorescence (pXRF) analysis.

The results revealed that the Altar Stone has a distinct composition compared to the other bluestones, including a much higher concentration of the element barium. The team said the discovery suggests that “it is time to broaden our horizons, both geographically and stratigraphically into northern Britain and also to consider continental sandstones of a younger age,” according to the study.

“Thomas grouped the Altar Stone with the other foreign stones, calling them the 'Blue Stones,’” Bevins told Motherboard. “But the Altar Stone is anomalous in its size, weight, and rock type, and there is no evidence for when the Altar Stone might have arrived at Stonehenge” whereas “the bluestones are thought to have arrived ca 2950 BC during the Stage 1 construction period.” 

“It might be that the Altar Stone arrived later and if so might have been brought from another area than Wales and also possibly by different people,” he continued. “This thinking was something of a game changer and led us to 'uncouple' the Altar Stone from the bluestones from Wales and led to our 'broadening horizons' approach.”

Indeed, the tantalizing find has sparked a geological treasure hunt for the true origin of the Altar Stone. Based on its composition, Bevins and his colleagues think that the stone could have come from Old Red Sandstone of the Midland Valley and Orcadian Basins in Scotland, or from deposits that date back some 250 million years to the Permian-Triassic eras in northern England. 

“The sites of interest are described in the paper, mainly northern England and Scotland but we need to develop our programme of fieldwork in those areas,” Bevins said. “We shall concentrate on those areas with known Neolithic activity as guided by our archaeological colleagues.”

Stonehenge is already considered an outlier among Neolithic structures because its bluestones were imported from Wales, whereas most other rock monuments from this period are built from local stones. Bevins and his colleagues note that “the bluestones in fact represent one of the longest transport distances known from source to monument construction site anywhere in the world” in the study.

Now, the researchers have proposed that the Altar Stone may hail from an even more remote region than its companion bluestones, which could be several hundred miles to the north. If Bevins and his colleagues are able to pinpoint the likely source of the special monument, it could reveal new insights about the purpose of the Altar Stone, the timeline of Stonehenge’s construction, and the lives of the people who built the world-famous structure.

 “It could well have significant implications for the movement and interactions of people in Neolithic times but that is an area that our archaeology colleagues will have views on,” Bevins said. “There are known links between Neolithic people (or their ‘culture’) from the northern British Isles and Neolithic Wessex and Stonehenge.”

“This long-distance connection occurred during the Stage 2 construction phase (c. 2500 BCE) so maybe the Altar Stone arrived during this period, well after the bluestones were erected?” the team concluded in the study. “The timing of these links needs to be further explored in order to try to discover when the Altar Stone arrived at Stonehenge. These considerations will inform the next phase of our investigations.”