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New research has revealed that the Stonehenge altar stone, which forms the heart of this ancient monument in southern England, was likely moved over 700 kilometres from what is now north-east Scotland almost 5,000 years ago.
The findings of a new study, published Wednesday in the journal Nature, overturn a centuries-old idea that the Altar Stone originated in modern-day Wales. The largest of the bluestones used to build Stonehenge, the Altar Stone is a thick block weighing 13,227 pounds (6 metric tons) that lies at the center of the stone circle.
“This stone has travelled an incredibly long way — at least 700 km — and this is the longest recorded journey for a stone used in a monument during that period,” study co-author Nick Pearce, a professor in the department of geography and earth sciences at Aberystwyth University in Wales, said in a statement. “The distance travelled is astonishing for that time.”
The research directly addresses one of Stonehenge’s many mysteries and also opens up new avenues for understanding the past, such as the connections between Neolithic peoples who left no written records, the study authors say.
According to researchers, the construction of Stonehenge began as early as 3000 BC and proceeded in several phases. It is thought that the altar stone was placed in the central horseshoe during the second phase of construction, around 2620 to 2480 BC.
The discovery of the stone’s origins suggests that ancient Britain and its people were much more advanced and capable of moving enormous stones, possibly via maritime routes, the study authors wrote.
Unraveling ancient secrets
Extensive research has been conducted into the types of stone used to assemble the iconic circle 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 construction of the monument. The monument stands on the southern edge of Salisbury Plain, which was inhabited as far back as 5,000 to 6,000 years ago.
The sarsens came from the West Woods near Marlborough, about 25 kilometres away, while some of the bluestones came from the Preseli Hills area of West Wales and are believed to have been the first stones to be placed at the site. Researchers have categorised the Altar Stone as one of the bluestones, but its origins have remained a mystery.
“Our discovery of the origins of the altar stone highlights a significant level of societal coordination during the Neolithic and helps to paint a fascinating picture of prehistoric Britain,” study co-author Chris Kirkland, professor and leader of the Timescales of Mineral Systems Group at Curtin University’s School of Earth and Planetary Sciences in Australia, said in a statement.
“Transporting such a huge load overland from Scotland to southern England would have been a huge challenge, suggesting a probable maritime shipping route along the coast of Britain. This implies long-distance trade networks and a higher level of social organisation than is generally thought to have existed in Neolithic Britain.”
To better understand the origins of the altar stone, the researchers analyzed the age and chemical composition of mineral grains from fragments of the stone itself.
The analysis revealed the presence of zircon, apatite and rutile grains in the fragments. The zircon was dated to between 1 billion and 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 to sediments and rocks across Europe, said study lead 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 northeastern Scotland, which were completely different from rocks found in Wales.
“The findings raise fascinating questions, given the technological limitations of the Neolithic, about how such a huge stone was transported over large distances around 2600 BC,” Clarke said.
For Clarke, the discovery was also a personal one. She grew up in the Preseli Hills in Wales, where some of the stones of Stonehenge came from.
“I first visited Stonehenge when I was 1 year old and now, at the age of 25, I have returned from Australia to help with this scientific discovery. You could say I have come full circle at the stone circle,” Clarke said.
But the discovery that the Altar Stone came from the area that is now Scotland raises a whole host of new questions.
“It is exciting to know that our chemical analysis and dating work has finally solved this great mystery,” study co-author Richard Bevins, an honorary professor in the department of geography and earth sciences at the University of Aberystwyth, said in a statement. “The hunt will continue to find out exactly where in north-east Scotland the Altar Stone came from.”
Joshua Pollard, a professor of archaeology at the University of Southampton, called the find “a fantastic result.” Pollard was not involved in the research.
“The science is good,” Pollard said. “This is the team that has been active in successfully obtaining the smaller Stonehenge bluestones using quite a sophisticated battery of techniques.”
Moving solid rocks
Today, the Altar Stone lies broken on the ground, with two stones from the collapsed Great Trilithon structure resting on top of it. A trilithon is a pair of vertical stones with a horizontal stone lying across the top. The horseshoe shape of Stonehenge includes five trilithons, but the Great Trilithon was aligned with the solstice axis, so on the winter solstice the sun would appear to set between the two stones.
However, researchers doubt whether the altar stone ever stood upright and what its purpose was.
“One suggestion is that stone was a witness to the dead, and so Neolithic people built stone circles as part of their rituals to respect their ancestors,” Bevins said.
Pollard called the Altar Stone a bit of an “anomaly, lying in what should be the most sacred piece of space within the monument.”
But how did the enormous Altar Stone actually end up on Salisbury Plain?
At the time, Britain was covered in forests and other impassable geographical features that would have made transporting the stone overland incredibly difficult, the study authors said. But a sea route could have made maritime transport possible, Clarke said.
“Although it seems incredible, Stonehenge itself is an incredible monument,” Pollard said. “It increasingly seems likely that the stones came from sources ancestral to those who created Stonehenge — it condenses historical lineage stories into one place.”
There are other examples of animals, artefacts and stones being transported, suggesting that cargo could have been transported across open water during the Neolithic period, the authors wrote in the study. Carved stone tools have been found across Britain, Ireland and continental Europe, including a large stone grinding tool found in Dorset County, in what is now central Normandy.
There is also evidence that formed sandstone blocks were transported by rivers in Britain and Ireland.
“While the aim of our new, empirical study was not to answer the question of how it got there, there are clear physical barriers to transport by land, but a daunting journey if it is by sea,” Pearce said. “There is no doubt that this Scottish source demonstrates a high level of social organisation in the British Isles during this period. These findings will have enormous implications for understanding Neolithic societies, their levels of connectivity and their transport systems.”
The authors agreed that some questions about Stonehenge may never be answered.
“We know why many ancient monuments were built, but the purpose of Stonehenge will always remain unknown,” Clarke said. “And so we have to turn to the rocks. It’s an enduring mystery.”
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