One of the Westcountry's most famous archaeological landmarks is being threatened by grazing cattle permitted by the Government's environment watchdog, campaigners have warned.
The Bronze Age stone monument, known as Men-an-Tol, has stood near Morvah, in West Cornwall, for up to 4,500 years.
It is listed as a scheduled monument with English Heritage describing it as "one of the most famous and mysterious" in Cornwall.
But campaigners fear it is now being damaged by cattle introduced onto the heathland under a Natural England agri-environmental scheme.
Ian McNeil Cooke, of the Save Penwith Moors action group, said: "On one of my recent, regular walks from my studio about half a mile away, I noticed cattle hair on the holed stone with hoof prints in the churned up ground surrounding all three stones.
"It is obvious that the cattle had been using the stones as convenient 'rubbing posts'."
He said several stones of the Bronze Age Tregeseal Circle, some three miles away, had been destabilised in a similar way when cattle were introduced in 2009.
Mr McNeil Cooke added: "It is obvious that the experience at Tregeseal Circle is being repeated at Men-an-Tol and that it is only a matter of time before damage is caused to this most famous and, arguably, most frequented ancient site in the Land's End Peninsula by locals – including parties of primary schoolchildren – and visitors from across the world.
"This is, of course, completely unacceptable to us and of extreme concern. English Heritage and Natural England have been asked what action will be taken to rectify the situation before it is too late and another scheduled ancient monument is destabilised and degraded."
The holed-stone is surrounded by folklore. Traditionally children were passed through the hole as a cure for rickets while one legend claims if a woman passes through the stone seven times backwards at full moon she will soon become pregnant.
A spokesman for English Heritage said the stones were set in concrete in the 1940s and reset in 1993 in response to concerns about soil erosion around the stones caused by visitor pressure.
He added: "We do not, however, expect cattle activity to cause damage to the stones or its setting, but will continue to monitor the site."
A Natural England spokesman said it was "committed to the sensitive management of both the natural and historic environment of West Penwith". He said: "In many areas of England 'conservation grazing' initiatives are successfully using cattle to graze sites in ways that help prevent important habitats and monuments becoming overgrown, while also enhancing wildlife interest and maintaining public access.
"We are aware of recent claims that the presence of grazing cattle in the area risks damaging the standing stones at Men-an-Tol. We are working with English Heritage to look into these claims and to ascertain whether there is any need to review grazing management for the area."