The Castlerigg stone circle, located in the northwestern county of Cumbria within the Lake District National Park, has long been a draw for tourists and was taken into guardianship in 1883—becoming one of the first prehistoric monuments in the country to receive state protection.

The monument is thought to be one of the oldest stone circles on the islands of Great Britain and Ireland, of which there are hundreds of known examples. England comprises most of the island of Great Britain, which it shares with the countries of Scotland and Wales.

Previous estimates based on circumstantial evidence have placed the construction of the Castlerigg stone circle at around 3000 B.C. or slightly earlier. But no solid dating work has been conducted at the site.

Now, Cumbrian archaeologist Steve Dickinson has shed new light on the monument’s possible age, proposing—based on his recent research—that at least part of the stone circle was erected around 3700 B.C., he told Newsweek.

The part Dickinson is referring to is known as the “Sanctuary”—a rectangle of large boulders, measuring around 23 feet by 15 feet, that projects into the middle of the stone circle from its eastern interior.

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While the function of the Sanctuary remains a mystery, the plan and size of this structure is similar to that of many small timber structures excavated in Ireland—and one recently uncovered in the English county of Yorkshire—all dated to the early Neolithic archaeological period, Dickinson said. In Britain and Ireland, this period lasted from around 4300 B.C. to 3300 B.C.

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The fact that the Sanctuary displays similarities to examples of small early Neolithic timber structures from Ireland is significant, according to Dickinson.

Radiocarbon dating of these timber structures suggests their construction began around 3730-3660 B.C. and that their use ended between roughly 3640-3600 B.C. This evidence is one of the reasons that Dickinson is proposing an early Neolithic date for the construction of the Castlerigg Sanctuary.

“The first part of my case for an early Neolithic Castlerigg is that the Castlerigg rectangular structure replicates the forms of some of the Irish examples. It monumentalizes them in stone,” he said.

“This monumentalizing in stone is a feature of the timber to stone transition widely regarded by many prehistorians as occurring across Britain and Ireland where enclosures and circles marked out with timber posts were turned into, or remodeled in, stone,” he said.

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“The second part of my early Neolithic case for Castlerigg is that the Sanctuary there was erected around 3700-3640 B.C.—following the use-life of the Irish structures,” Dickinson said.

Dickinson’s proposal has not yet been published in a peer-reviewed journal, and will likely require further research to confirm it. But if the theory is correct, it would date the Sanctuary to around 700 years before the first phase of construction at Stonehenge, which occurred around 3000-2900 B.C.—long before the large stones made an appearance.