Soil analysis at an ancient site in Britain associated with King Arthur has revealed that the structure is unlikely to date to the Middle Ages because it has been underground for thousands of years. King Arthur’s Hall in Cornwall, England, is actually 5,500 years old, according to a new estimate. This suggests that the rectangular mound of earth and stone is five times older than the previous estimate of around 1000 AD.

This would shift the date of construction to the Neolithic period and may also require changing the name of the site. Although few experts believe that King Arthur was an actual historical figure, his legendary appearance is associated with a period closer to the Dark Ages and the Middle Ages than to prehistory.

The key to the updated dating is the Optical Stimulated Luminescence (OSL) method, which measures the persistent effect of background radiation on the location of electrons in buried minerals. Analyzing the mineral’s glow when excited allows scientists to determine how long it has been since it last saw sunlight.

“It is extremely exciting that we can finally determine the construction date of this mysterious monument, which has previously been the subject of myth and legend,” says archaeologist Tim Kinnaird from the University of St Andrews in the UK.

The site, measuring 47 meters x 20 meters (154 ft x 66 ft), is located in Bodmin Marsh. It is surrounded by stone blocks up to 1.8 meters (6 ft) high, known as orthostatic, although most no longer stand upright.

It was previously thought that this was some kind of camp or cattle pen, but the new history of King Arthur’s Hall may require a rethinking of what the earthworks might have been used for.

“We must now look at the monument in the context of the prehistoric landscape of Bodmin Moor and other moorland structures that may have been important at the time,” says Kinnaird. “All this points to a rich Neolithic landscape suggesting active community life on the steppe, which needs further investigation.”

According to the BBC, researchers believe there is much more to be found in this area, so visitors should be careful not to damage any part of the structure. The area is currently on the Historic England list at Risk due to potential damage from overgrown vegetation, livestock and humans.

One of the difficulties in understanding what King Arthur’s Hall was actually used for and by whom is that it is a unique place. There is nothing else that can be directly compared to this intriguing arrangement of earth and stone.

“There’s nothing like it anywhere,” lead archaeologist James Gossip of the Cornwall Archeology Unit told Esther Edley in an interview with The Guardian. “Neither at that time nor in the later prehistoric period was anything resembling a rectangular earth and stone embankment with a stone orthostat built built in it. There is no other parallel.”