Excavations are being carried out to save a 'secret' stone circle - described as 'Cornwall's ancient sacred heart'.

The unique prehistoric ritual site of Castilly Henge is largely unknown, but described by experts as one of the UK's most important late Neolithic sites.

Located just off the A30 near Bodmin, the henge is believed to have been built about 3000 to 2500 BCE.

The substantial oval earthwork includes an external bank and internal ditch, which would have formed an amphitheatre-like setting for gatherings and ritual activities.

Recent surveys undertaken by Historic England’s Archaeological Investigation Team discovered traces of a now-removed possible stone circle in the middle of the henge. Not all henges contain stone circles, and there is only one other known to survive in Cornwall.

Cornwall Heritage Trust launched a fundraising appeal to secure its future.

Earlier this year, a major project designed to reveal its secrets was given the green light thanks to a £42,990 grant from The National Lottery Heritage Fund.

A four-week archaeological excavation scheduled for October is hoped to help understand more about the monument’s character, date and potential later reuse.

Dr Olaf Bayer, senior archaeological investigator for Historic England said: "We're delighted to be working with partners at Castilly Henge to grow our collective understanding of this special prehistoric site.

"Following our discovery of the remains of a previously unknown possible stone circle in 2022, we're back to carry out the first excavation on the site in over 60 years.

"The technology available to us today will enable us to take a closer look at the evidence and hopefully find out more about how and exactly when the site was used. We're excited that volunteers and the local community will have the opportunity to get involved in the project.

"The henge is currently at risk due to the threat posed by invasive vegetation.

"Modern development of the nearby road infrastructure and local service network, which lie within metres of the site, also pose potential risks.

"To combat these risk factors, the final stage of the project will involve the creation of management plans aimed at enhancing the biodiversity of the field and the condition of the monument, as well as ensuring sustainable management in the future."

Its significance continued into the Early Bronze Age (c.2400-1500 BCE) when several high-status burial mounds or barrows were built close by.

Cathy Woolcock, Cornwall Heritage Trust chief executive officer, said: “The henge has been at risk for some time – a threat which urgently needs to be addressed before this special place and the secrets it holds are potentially lost.

“Our charity has been protecting historic landscapes and monuments across Cornwall for the last 40 years.

"We have a strong track record of giving these special places the archaeological and land management expertise they need and have helped save a number from the Heritage at Risk Register."

Previous researchers have suggested that the site may have been used as a medieval open-air theatre, known as a plen-an-gwari, and later as a battery during the English Civil War.