Stonehenge: Mysterious Origins of ‘Unique’ Altar Stone Finally Revealed

A research team has unraveled the mysterious origins of a “unique” stone that forms a key part of Stonehenge, the world-renowned prehistoric monument in southwest England, a study reports.
The study, published in the journal Nature, demonstrates that the iconic 6-ton “Altar Stone” likely came from what is now northeast Scotland—at the opposite end of the island of Great Britain from the monument’s location.
For more than a century, it was thought that the Altar Stone, which sits at the heart of the prehistoric monument, originated from Wales, which is in Great Britain’s southwest. But some studies published in the past few years—including research conducted by the Nature study’s authors—cast doubt on this hypothesis. Thus, the true origin of the Altar Stone remained an open question—until now.
Stonehenge is a Neolithic stone monument in the county of Wiltshire. Construction of the monument, which consists of several large stones (known as megaliths) arranged in a circle shape, is thought to have begun around 5,000 years ago, with several changes and additions made to the structure over the next two millennia.
“The Altar Stone is unique in the monument, in terms of its size, weight, rock type and position in the monument. However, little is known about the Altar Stone—when it arrived on site, whether it ever stood erect or was always recumbent—and as a consequence little is known about its purpose,” Richard Bevins, an author of the Nature study, told Newsweek.
While the date of the Altar Stone’s arrival is unclear, it may have been placed within the central horseshoe of stones during the second construction phase, around 2620 to 2480 B.C.
Previous research at Stonehenge had identified two main types of stone used in the construction of the monument: the so-called sarsen stones and the bluestones. Most of the sarsens appear to have been sourced from the West Woods, near the modern Wiltshire town of Marlborough, which is around 15 miles away. Most of the bluestones had been shown to originate from west Wales.
The Altar Stone, made from sandstone, had traditionally been grouped with the other smaller, bluestones.
“The original proposal for a west Wales origin for the Altar Stone dates back over a century. In 1923, geologist H.H. Thomas suggested a west Wales origin, in the belief that all the bluestones came from a restricted part of the country,” said Bevins, who is with the Department of Geography and Earth Sciences at Wales’ Aberystwyth University.
In the latest study, the research team analyzed the age and chemistry of mineral grains within sample fragments of the Altar Stone, which measures roughly 16 by 3 feet and is around 20 inches thick.
Following this analysis, the team found that the age and chemistry of these grains were statistically indistinguishable from those in rocks from outcrops in northeast Scotland, and they were clearly different from Welsh bedrock.
The team’s analysis revealed a distinct chemical fingerprint indicating that the Altar Stone came from the Orcadian Basin, a regional-scale geological depression in northeast Scotland, located more than 400 miles away from Stonehenge.
“The age dating that has been undertaken in the Curtin University laboratories has shown there to be a remarkable similarity between the geological fingerprint of the Old Red Sandstone rocks from the Orcadian Basin in northeast Scotland and the Altar Stone. We are highly confident of the correlation,” Bevins said.
The latest geological findings raise fascinating and important new questions: Namely, why and exactly how was the massive Altar Stone transported from the far north of Scotland to the Stonehenge site hundreds of miles away, given the technological constraints of the Neolithic period?
The results suggest the presence of long-distance trade networks and a higher level of societal organization than is widely understood to have existed in Neolithic Britain, enabling unexpectedly advanced transportation methods, the authors suggest. Land transport would have been extremely challenging, owing to the geographical features of Britain and the forested nature of the island at the time. This means a sea route was more likely.
Jake Ciborowski, a geologist at Ireland’s University of Galway who has participated in Stonehenge research but was not involved in the latest study, told Newsweek that the conclusion regarding the origin of the Altar Stone in the Nature paper is “absolutely supported” by the “high-quality” data.
“I think that the Altar Stone source has been identified in this work,” Ciborowski said. “It’s a huge part of the Stonehenge story in itself.”
But Ciborowski said he was less certain about whether the Altar Stone was quarried from rocky outcrops in northeast Scotland and then shipped by boat to the Stonehenge site.
“There is no direct archaeological evidence of this—no quarry site has been identified, but that doesn’t mean there isn’t one to find,” he said.
“Also, Scotland was heavily glaciated during the last ice age, and a lot of rocky material on the surface was moved around by the ice,” he continued. “The authors say this is unlikely in the paper, but there is a possibility that the Altar Stone might have been originally moved by ice some of the way towards the south and then moved the rest of the way by humans. But that is speculation.”
If the Stonehenge builders did quarry the Altar Stone and transported it all the way to the site, “it is an astonishing achievement and says much about their ingenuity and importance they placed on sourcing materials for specific cultural purposes,” Ciborowski said.
“We already have strong evidence they moved different rock types huge distances…so why not the Altar Stone from [the Orcadian Basin]? Why specifically might they have picked this rock from so far away? Who knows? It’s speculation beyond my comfort,” he said.
With the Altar Stone’s origin identified as the Orcadian Basin in northeast Scotland, the task now is to pin down where exactly in this region it came from.
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Clarke, A.J.I., Kirkland, C.L., Bevins, R.E., Pearce, N.J.G., Glorie, S., & Ixer, R.A. (2024). A Scottish provenance for the Altar Stone of Stonehenge. Nature, 632(8025).
Bevins, R.E., Pearce, N.J.G., Ixer, R.A., Pirrie, D., Ando, S., Hillier, S., Turner, P., & Power, M. (2023). The Stonehenge Altar Stone was probably not sourced from the Old Red Sandstone of the Anglo-Welsh Basin: Time to broaden our geographic and stratigraphic horizons? Journal of Archaeological Science: Reports, 51(104215).