by Scientists say they have cracked the secret of the 6-tonne rock at the center of Stonehenge – a discovery that only deepens the mystery of the site.
The ancient monument’s “altar stone,” a sandstone rock at its center, likely originated in present-day Scotland, according to a study published Wednesday in the journal Nature. That means it was dragged more than 450 miles to southern England – much further than any other stone at Stonehenge with a known origin.
The result raises profound questions. The researchers suspect that the altar stone was installed about 4,500 years ago, which means that Neolithic people were able to move the rock hundreds of miles – long before the invention of light wheels, so to speak.
The revelation also suggests that cultural and social structures were more intertwined in the British Isles at the time than previously understood, and that Neolithic people were able to complete complex projects with relatively simple tools.
The discovery was based on an analysis of the age of mineral grains within the sandstone rock. After profiling the ages of the grains, the researchers were able to compare the altar stone’s age “fingerprint” to a database of sandstone samples across Britain and nearby places such as Brittany, France.
“With a high level of statistical certainty, in fact, more than 95% confidence, we can link the age spectrum to a very specific area in north-east Scotland,” said Chris Kirkland, co-author of the study and associate professor. Earth and planetary sciences at Curtin University in Australia.
The region Kirkland was referring to, the Orcadian basin, includes the Orkney islands, which are famous for their elaborate stone circles.
“The specific reason this matter was brought, we can’t answer that directly,” Kirkland said. “All we know is that it is a 6 and a half ton piece of rock that has come from 750 kilometers away. That, in itself, tells us a lot about Neolithic society and its connectivity.”
Stonehenge – a UNESCO World Heritage site and one of the best preserved prehistoric megalithic monuments – is surrounded by large sandstone tablets called “sarsens.” These, in turn, support stone lintels — horizontal spans also made of rock, some slotted together with joints. Within the sarsen outline is an inner circle of “bluestones” with an additional horseshoe shape within that circle.
The sarsens are thought to have come from about 15 miles north of the Stonehenge site, while the bluestones came from Wales, about 140 miles away.
The new study concerns the central altar stone: a tablet-shaped rock about 16 feet long, which shows evidence of having been shaped by human tools. There are other Stonehenge tablets on top of the altar rock now, apparently in disrepair.
“It’s a special stone for whatever reason,” said David Nash, professor of physical geography at the University of Brighton, who has studied Stonehenge but was not involved in the new research. “It’s a very different stone from all the other stones at the monument.”
Kirkland and his fellow researchers examined three ways in which the altar stone could have traveled from Scotland to Stonehenge. The first is that it was glacial ice transport during the Ice Age, but the authors of the study do not think that is the correct explanation. The second is that people moved it over land, but the team suspects that the forested terrain would be too challenging.
The third option, which they think is most likely, is that the stone was transported in a boat. There is evidence of maritime navigation around this time period — when England had another shore today.
Nash said the authors reached “sound conclusions” about the origins of the altar stone.
“What they have done is really interesting,” he said, adding that their findings strengthen evidence that Neolithic people traveled across Britain and were part of a broad social framework. “It’s clear that there are social structures, there are connections, the communication of ideas is very clear.”
Stonehenge is one of about 1,300 ancient stone circles in existence, according to the British Museum. Researchers think the site’s stones were shaped by hand tools and raised with winch and pulley systems. They are set to align with the movements of the sun and the summer and winter solstices.
Experts suspect that Neolithic people used these sites for ceremonies or rituals, but the details are lost in time. It is not clear what made the altar stone particularly special.
“Millionaires today cover their houses with Carrara marble from Italy, and I’ll never understand why they do that, so it’s just a mystery,” said Anthony Clarke, lead author of the new study and a doctoral student at the University of Curtin. “People have always been interested in finding the perfect rock, and perhaps the Neolithic Britons are the same, so their motivations are lost in time.”
The researchers said they hope, as a next step, to find the outcrop or region where the rock came from, but the basic measurement will likely remain.
“They put a huge value on bringing that stone 700, 800, 900 kilometers,” said Nick Pearce, another co-author of the study and professor of geography and Earth Sciences at Aberystwyth University in Wales. “However, they took it with them, it meant something to them. What did it mean? Why did they matter so much? It gives us all something to think about.”
This article was originally published on NBCNews.com
