Stone circle discovered inside Cornwall henge

This represents a rare find for the area: the only other known Cornish henge monument with a stone circle is Stripple Stones on Bodmin Moor.

Investigations at Castilly Henge, a late Neolithic earthwork near Bodmin in Cornwall, have revealed the remains of a previously unknown stone circle.

The c.4,500- to c.5,000-year-old henge (below) survives as a 68m by 62m enclosure at the summit of a low rise called Castle Hill, near the source of the Luxulyan River. The monument is an oval, with a level interior measuring 48m by 28m, and it is surrounded by a deep internal ditch and an external bank up to 1.6m high in places. Such sites are often interpreted as places for prehistoric gatherings and ritual activity, and it has been suggested that Castilly Henge was remodelled in the medieval period as a theatre or ‘playing place’ (from the Cornish plen-an-guary), before it was repurposed again – this time as a gun battery – during the English Civil War.

IMAGE: © Historic England/CAU.

The henge is a Scheduled Ancient Monument, but is also one of nearly 5,000 historic sites and structures across England that Historic England has deemed to be ‘at risk’. In this case, it is located in an area that makes it difficult to look after, and overgrown bracken and other vegetation is now threatening buried archaeological deposits. In 2021, though, the henge was included in a Monument Management Scheme (MMS) – a partnership between Historic England and the Cornwall Archaeology Unit (CAU) focused on conserving and repairing monuments on the Heritage at Risk Register.

As part of the MMS, CAU coordinated a team of 13 volunteers who helped clear the site of vegetation last winter. This enabled Olaf Bayer and Elaine Jamieson from Historic England’s Archaeological Survey and Investigation team to carry out a detailed analytical earthwork survey of the remains of the henge’s bank and ditch. This work, which has allowed a much better understanding of the henge’s original form and of later modifications to the site, led Olaf to suspect that there might be a stone or timber circle at the centre of the monument. To find out more, Neil Linford and Andy Payne from Historic England’s Geophysical Survey team carried out a combination of earth-resistance, magnetic, and ground-penetrating radar (GPR) surveys – the first modern archaeological investigations to be undertaken at the site.

The earth-resistance survey revealed seven regularly spaced ‘pit’-shaped anomalies, at least three of which were associated with potential ‘stone’ anomalies shown in the GPR survey. These have been interpreted as traces of a stone circle at the centre of the henge; some of the stones appear to have been pushed beyond the pits, while others have either not been detected by the survey or removed from the site entirely. This represents a rare find for the area: the only other known Cornish henge monument with a stone circle is Stripple Stones on Bodmin Moor, around 12 miles north-east of Castilly Henge.

Olaf, Archaeological Investigator for Historic England, said: ‘It has been rewarding to focus attention on Castilly Henge for the first time since the 1960s. Our recent work, using only non-intrusive techniques, has raised new questions about the monument and will provide an interesting starting point for any future research.’

There are currently no plans for further archaeological research work at the site, which now has fencing allowing it to be grazed and better managed. Researchers are evaluating aerial photographs and LiDAR images of the henge and its immediate landscape, and the results of the most-recent analyses will be published in a Historic England research report later this year.

For more details, linked to previous investigations, see