Century-old theory of where Stonehenge’s Altar Stone came from overturned by new study

(CNN) — Stonehenge’s Altar Stone, which lies at the heart of the ancient monument in southern England, was likely transported over 435 miles (700 kilometers) from what’s now northeastern Scotland nearly 5,000 years ago, according to new research.

The findings of a new study, published Wednesday in the journal Nature, overturn a century-old idea that the Altar Stone originated in current-day Wales. The Altar Stone, the largest of the bluestones used to build Stonehenge, is a thick block that weighs 13,227 pounds (6 metric tons) and lies at the center of the stone circle.

“This stone has travelled an awful long way — at least 700 km — and this is the longest recorded journey for any stone used in a monument at that period,” said study coauthor Nick Pearce, a professor in the department of geography and Earth sciences at Aberystwyth University in Wales, in a statement. “The distance travelled is astonishing for the time.”

The research directly addresses one of Stonehenge’s many mysteries and also opens up new avenues into understanding the past, including the connections between Neolithic people who left behind no written records, the study authors said.

Construction on Stonehenge began as early as 3000 BC and occurred over several phases, according to the researchers, and the Altar Stone is believed to have been placed within the central horseshoe during the second construction phase around 2620 to 2480 BC.

The discovery of the stone’s origin suggests that ancient Britain and its citizens were far more advanced and capable of moving massive stones, possibly through maritime means, the study authors wrote.

Unlocking ancient secrets

Substantial research has focused on the types of stone used to assemble the iconic circle located in Wiltshire over the years, and previous analysis has shown that bluestones, a type of fine-grained sandstone, and silicified sandstone blocks called sarsens were used in the monument’s construction. The landmark sits on the southern edge of Salisbury Plain, which was inhabited as early as 5,000 to 6,000 years ago.

The sarsens came from the West Woods near Marlborough, located about 15 miles (25 kilometers) away, while some of the bluestones originated from the Preseli Hills area in west Wales, and are thought to be the first stones placed at the site. Researchers have categorized the Altar Stone with the bluestones, but its origins have remained a mystery until now.

“Our discovery of the Altar Stone’s origins highlights a significant level of societal coordination during the Neolithic period and helps paint a fascinating picture of prehistoric Britain,” said study coauthor Chris Kirkland, a professor and leader of the Timescales of Mineral Systems Group at Curtin University’s School of Earth and Planetary Sciences in Australia, in a statement.

“Transporting such massive cargo overland from Scotland to southern England would have been extremely challenging, indicating a likely marine shipping route along the coast of Britain. This implies long-distance trade networks and a higher level of societal organisation than is widely understood to have existed during the Neolithic period in Britain.”

To better understand the origin of the Altar Stone, the researchers analyzed the age and chemistry of mineral grains from fragments of the stone itself.

The analysis revealed the presence of zircon, apatite and rutile grains within the fragments. The zircon was dated to between 1 billion to 2 billion years ago. But the apatite and rutile grains came from between 458 million and 470 million years ago.

The team used the analysis of the ages of the mineral grains to create a “chemical fingerprint” that could be compared with sediments and rocks across Europe, said lead study author Anthony Clarke, a doctoral student from the Timescales of Mineral Systems Group within Curtin’s School of Earth and Planetary Sciences. The grains best matched a group of sedimentary rocks known as Old Red Sandstone found in the Orcadian Basin in northeast Scotland, which differed completely from stones found in Wales.

“The findings raise fascinating questions, considering the technological constraints of the Neolithic era, as to how such a massive stone was transported over vast distances around 2600 BC,” Clarke said.

The discovery was also a personal one for Clarke, who grew up in the Preseli Hills in Wales, the origin point of some of Stonehenge’s stones.

“I first visited Stonehenge when I was 1 year old and now at 25, I returned from Australia to help make this scientific discovery — you could say I’ve come full circle at the stone circle,” Clarke said.

But determining that the Altar Stone originated from what’s now Scotland raises a multitude of new questions.

“It’s thrilling to know that our chemical analysis and dating work has finally unlocked this great mystery,” said study coauthor Richard Bevins, honorary professor in the department of geography and Earth sciences at Aberystwyth University, in a statement. “The hunt will still very much be on to pin down where exactly in the northeast of Scotland the Altar Stone came from.”

Joshua Pollard, a professor of archaeology at the University of Southampton, called the finding “a great result.” Pollard was not involved in the research.

“The science is good,” Pollard said. “This is the team that have been active in successfully sourcing the smaller Stonehenge bluestones using a pretty sophisticated battery of techniques.”

Moving massive stones

Today, the Altar Stone lies broken on the ground, with two stones from the collapsed Great Trilithon structure resting atop it. A trilithon is a pair of vertical stones with a horizontal stone lying across their tops. Stonehenge’s horseshoe shape includes five trilithons, but the Great Trilithon was aligned with the solstice axis, so on winter solstice, the sun appeared to set between the two stones.

But researchers question whether the Altar Stone once stood upright, as well as the purpose it once served.

“One suggestion is that stone was a testimony to the dead, and so Neolithic people built stone circles as part of their rituals for respecting their ancestors,” Bevins said.

Pollard referred to the Altar Stone as a bit of an “anomaly, lying recumbent in what should be the most sacred bit of space inside the monument.”

But how exactly did the hulking Altar Stone arrive on the Salisbury Plain in the first place?

At the time, Britain was covered with forests and other impassable geographical features that would have made transporting the stone over land incredibly difficult, the study authors said. But a sea route could have allowed for marine transport, Clarke said.

“While it seems incredible, Stonehenge is itself an incredible monument,” Pollard said. “Increasingly it looks as though the stones are drawn from sources ancestral to those who created Stonehenge — it kind of condenses historic lineage stories in one place.”

There are other examples of animals, items and stones being transported that suggest cargo could be shipped over open water during the Neolithic Period, the authors wrote in the study. Quarried stone tools have been found throughout Britain, Ireland and continental Europe, including a large stone grinding tool found in the county of Dorset that came from what’s now central Normandy.

There is also evidence that shaped sandstone blocks were transported on rivers in Britain and Ireland.

“While the purpose of our new, empirical research was not to answer the question of how it got there, there are obvious physical barriers to transporting by land, but a daunting journey if going by sea,” Pearce said. “There’s no doubt that this Scottish source shows a high level of societal organisation in the British Isles during the period. These findings will have huge ramifications for understanding communities in Neolithic times, their levels of connectivity and their transport systems.”

The authors agreed that some questions about Stonehenge may never be answered.

“We know why a lot of ancient monuments were built, but the purpose of Stonehenge will always be unknown,” Clarke said. “And so we have to turn to the rocks. It’s an enduring mystery.”

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