An analysis on the soil at an ancient site in the UK linked to King Arthur has found construction isn't likely to be medieval after all, having sat buried beneath the ground for thousands of years.
The new estimate suggests King Arthur's Hall, in Cornwall in England, is in fact 5,500 years old. That makes the rectangular bank of earth and stone five times older than an earlier assessment, which dated it back to around 1000 AD.
It shifts the date of the structure back to the Neolithic, and may necessitate a name change for the location as well. While few experts believe King Arthur was a real historical figure, his mythical adventuring is associated with a period closer to the dark and middle ages than the prehistoric era.
Key to the revised dating is a technique called optically stimulated luminescence (OSL), which measures the steady effect of background radiation on the positions of electrons in buried minerals. An analysis of the mineral's glow when stimulated tells scientists how long it's been since it last saw sunlight.
"It's extremely exciting that we've finally been able to date construction of this enigmatic monument, previously grounded in myths and legends," says archaeologist Tim Kinnaird, from the University of St Andrews in the UK.
The site measures 47 meters by 20 meters (154 feet by 66 feet), and sits on Bodmin Moor. It's surrounded by stone blocks known as orthostates that are up to 1.8 meters (6 feet) high, though most of them are no longer standing upright.
Previously speculated to be some kind of camp or cattle pound, the new date for King Arthur's Hall could demand a rethink about what the earthworks may have been used for.
"We now need to consider the monument within the context of Bodmin Moor's prehistoric landscape, and the other structures on the moor that might have been significant at the time," says Kinnaird.
"This all alludes to a rich Neolithic landscape, evidencing an active community on the moor, which requires further investigation."
As the BBC reports, the researchers think there's more to be discovered at the site, meaning visitors should be careful not to disturb any part of the structure. The site is already on the Historical England At Risk register, because of potential damage from growing vegetation, livestock, and people.
Part of the problem in figuring out what King Arthur's Hall was actually used for – and by whom – is that it's a unique spot. There's nothing else to directly compare to this intriguing arrangement of earth and stone.
"There isn't another one of these anywhere," lead archaeologist James Gossip, from the Cornwall Archaeological Unit told Esther Addley at The Guardian.
"There is nothing built at that time or subsequently in prehistory that is a rectangular earth and stone bank with a setting of stone orthostats around the interior. There is no other parallel."