Stonehenge, the Neolithic stone circle on Salisbury Plain in southern England, has captivated archaeologists, antiquarians and sightseers for centuries. In the twelfth century, cleric Henry of Huntingdon described the haunting assemblage as one of the great wonders of England, adding that no one knew who built it or why. Over the millennia, its building has been variously attributed to the Romans, the Vikings, the Saxons, druids — and even Merlin, King Arthur’s court magician who, by one medieval telling, used his wizardly powers to whisk the stones over the seas from Ireland.
The ancient ritual meaning of Stonehenge is still a mystery, but researchers are one step closer to understanding how the famous stone circle was created.
The unique stone lying flat at the center of the monument was brought to the site in southern England from near the tip of northeast Scotland, researchers reported Wednesday in the journal Nature. It’s not clear whether the 16-foot (5-meter) stone was carried by boat or across land — a journey of more than 460 miles (740 kilometers).
The discovery has thrilled archaeologists. “It’s a fantastic study with some big implications,” says Jim Leary, a field archaeologist at the University of York, UK. The findings increase researchers’ understanding of the henge’s builders, people of a Neolithic society that lived in Britain between about 4300 and 2000 BC.
“It’s a surprise that it’s come from so far away,” said University of Exeter archaeologist Susan Greaney, who was not involved in the study.
For more than a hundred years, scientists believed that Stonehenge’s central sandstone slab — long called the “altar stone” — came from much closer Wales. But a study last year by some of the same researchers showed that the stone didn’t match the geology of Wales’ sandstone formations. The actual source of the stone remained unknown until now.
For the study, the team was not permitted to chip away rocks at the site, but instead analyzed minerals in bits of rock that had been collected in previous digs, some dating back to the 1840s. They found a match in the sandstone formations of Orcadian Basin in northeast Scotland, a region that includes parts of the tip of the Scottish peninsula as well as the Orkney Islands.
“That geological ‘fingerprint’ isn’t repeated in any other area of sediment in the U.K.,” said Aberystwyth University geologist Nick Pearce, a study co-author.
Greaney said the difficult logistics of moving the stone such a long distance show a high level of coordination and cultural connection between these two regions of ancient Britain.
Stonehenge was constructed around 5,000 years ago, with stones forming different circles brought to the site at different times. The placement of stones allows for the sun to rise through a stone “window” during summer solstice. The ancient purpose of the altar stone — which lies flat at the heart of Stonehenge, now beneath other rocks — remains a mystery.
The culture flourished in the Orkney Islands in Scotland in the centuries before Stonehenge was completed, and archaeologists have been captivated by their art and pottery traditions, as well as their monuments they erected. “They built monuments that pointed to these wide connections,” says Leary. “It seems to me these later Neolithic people were master geologists, able to read stone and understand where it originated and the connections it symbolized.”
“Stonehenge isn’t a settlement site, but a place of ceremony or ritual,” said Heather Sebire, senior curator at English Heritage, who was not involved in the study. She said that past archaeological excavations had not uncovered evidence of feasting or daily living at the site.
Previous research has shown cultural connections — such as similarities in pottery styles — between the area around Stonehenge and Scotland’s Orkney Islands. Other stones at Stonehenge came from western Wales.
While Britain is dotted with other Neolithic stone circles, “the thing that’s unique about Stonehenge is the distance from which the stones have been sourced,” said Aberystwyth University’s Richard Bevins, a study co-author.
Stonehenge’s iconic slabs are divided into two groups. About 30 tall, upright sarsens make up the outer and inner circles, most pairs capped by shaped lintel stones. Studies have pinpointed the origin of the sarsens to the Marlborough Downs, about 25 kilometres away. The other blocks include about 80 bluestones, which analyses suggest came from the Mynydd Preseli mountains in western Wales.
The Altar Stone, a six-tonne chunk of sandstone that measures 5 metres by 1 metre, is the largest of the bluestones (see ‘Buried altar’). It was probably named by the seventeenth-century architect Inigo Jones, who commented on its recumbent appearance, although it is not known whether the block once stood upright. Previous research had suggested that the Altar Stone might also have come from Wales.
The latest study uses dating and chemical analysis of tiny zircon, rutile and apatite crystals from fragments of the Altar Stone to trace its source to the Old Red Sandstone formations in the Orcadian Basin in the northeast of Scotland and the Orkney Islands (see ‘Stone sources’). “It’s like finding a fingerprint,” says Anthony Clarke, a geochronologist at Curtin University in Perth, Australia, who led the study. “It was a perfect match for the Orcadian Basin and no match at all for anything in England or Wales.”
The zircon, rutile and apatite crystals are nearly indestructible, says Clarke, and are essentially recycled over aeons as mountains are built and worn down. The researchers dated the crystals to one billion years ago. Their presence in the Altar Stone is a legacy of a time before the continents drifted into their present positions. What is now Scotland was then part of an ancient continental segment called the Laurentian Shield, which is in present-day eastern Canada. Old Red Sandstones found elsewhere in Britain won’t contain such ancient crystals, because the rest of Britain was part of a younger continental segment called East Avalonia. “The Altar Stone could only have come from Scotland,” says Clarke, who grew up in the Mynydd Preseli mountains, where the other bluestones are from.
How the stone was ferried to southern England from Scotland or the Orkney Islands is already a matter of lively debate. Geologists have ruled out the idea that glaciers might have transported it. “There is simply no evidence for it,” says Clarke. “This was brought here by human agency.”
Whether the people of Neolithic Britain moved it by land or by sea is an open question. The land between Scotland and Stonehenge is rugged, making for a difficult trek — but a sea voyage, too, would have been risky.
“I can’t see them risking such a valuable cargo on such a hazardous journey,” says Pitts.
By contrast, Leary thinks a sea journey is the most likely. “We seriously underestimate their abilities and technologies,” he says. “We’ve never found any of their boats, but we know they were able to transport cattle, sheep and goats by sea.”
Whatever the method, scientists agree that the transport of such an important stone would probably have been a spectacle, with people living along the route turning out to witness the event.
The discovery that the Altar Stone came from Scotland or Orkney isn’t the end of the matter. “We still need to narrow down exactly where it was obtained,” says study co-author Rob Ixer, a geologist at University College London who has spent decades tracing the sources of Stonehenge’s monoliths.
“Tracing these stones has always been like chasing a rabbit — it’s always bounding ahead of you. I think we’re going to have plenty more surprises as we go along.” (AP/Nature)
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