The area which will experience a total eclipse includes the highest number of Neolithic monuments in Britain, including a 6,000-year-old hill fort. This is posing a major worry for archaeologists.

Revellers urged to respect sites

The BBC's Tim Hirsch: "Visitors unaware of the archaeological treasures."

Both they and the pagans fear the monuments could become a focus for the sort of scenes witnessed at Stonehenge in June, when revellers and the police clashed during the last summer solstice of the millennium.

"We hope very much that there isn't an excuse for the for the sorts of events that happened at Stonehenge because there won't be, as far as I'm aware, a heavy police presence," said Andy Norfolk, a pagan.

"There will be people like myself encouraging people to treat the sites with respect. And we hope that taking this very positive approach will actually avoid any trouble."

Illegal rave sparks concern

One of Cornwall's most popular monuments is the Men-An-Tol stone, near Penzance, which local folklore claims has healing properties for anyone who crawls through it.

Summer solstice celebrations at Stonehenge led to clashes with police

English Heritage has learned there are plans to hold an illegal festival on the site, billed as Men-An-Tol tribal gathering.

English Heritage spokeswoman Ann Preston-Jones expressed concern that this could attract large numbers of people who were "not going to be that careful about the stones".

Others fear revellers will simply be unaware of the archaeological treasures hidden in the ground.

Stephen Heartgraves of the Cornwall Archaeology Unit said it was easy to imagine how thousands of people walking on a site could erode it, destroying vital evidence of ancient Cornish tribes' activities.

The hope is that the vast majority of visitors will observe the eclipse code being posted up at many of the ancient sites.

But one of the rules - no fires - has already been broken at Men-An-Tol, risking its destruction.