THE work of prehistoric sculptors who carved intricate designs into age-old rocks has fascinated archaeologists for decades.

Many of the carvings have withstood the effects of industry and the weather and can still be found on hilltops and in valleys across the country.

The meanings of the complex symbols have never been discovered, but a newly-published book is aiming to shed some light on the phenomenon.

The publication pulls together information on all known rock art on the North York Moors.

Stone Age people used the moors not only as a hunting ground, but also as a place to bury their dead, and there are thousands of cairns and barrows that cover the moors area.

Many burial places include carved rocks.

The book, Prehistoric Rock Art in the North York Moors, has been written by Paul Brown, from Darlington, and Graeme Chappell, from Tadcaster, North Yorkshire.

They have spent the past ten years carrying out a painstaking investigation into the rocks, many of which are covered by heather and gorse bushes.

Mr Brown, 61, said: "Nobody knows what the carvings mean. I have said to other people, even if I hit on the exact meaning of them, there is no way I could prove it.

"It has become an enigma. They are so complex. Some of the patterns they have used are very intricate. You can get cross hatches and all kinds of symbols which, put on to the rock, are quite attractive."

The carvings date back to between 4,500 and 4,000 years, and are often found in clusters.

Mr Brown, who is a television engineer, said: "It may be that the spot is very significant in the landscape and when groups of people visited they carved in to the rock.

"It may be an area where it is a temporary camp. It could have been an area where they buried one of their ancestors. We just don't know."

He has also studied rock art in Teesdale, Cumbria and Scotland.

The book is available from local bookshops and from Tempus Publishing.