The intriguing abstract shapes of Britain's prehistoric rock art - rings and hollows, zigzags and arcs - are indecipherable now, and largely unknown to the public.
The Stone Age people who carved the designs on sandstone slabs and granite boulders left a large number of them across the country, with about 2,500 sites currently known.
And now a major effort is under way to catalogue the drawings, find more of them and learn how to conserve them. It is hoped also to bring them to the public's attention.
Britain cannot boast the wonderful prehistoric cavepaintings of wild animals found at Lascaux and other sites in southern France and Spain. We have but a few representations of animals, such as the goats or deer carved on the face of what was an ancient rock shelter at Goat's Crag in north Northumberland.
But we do have an extraordinary amount of mysterious, carved and scratched abstract shapes that would not look out of place in a late-period Picasso, and which clearly once held an important meaning.
"This stuff was created between 4,000 and 5,000 years ago by the first farming communities in Britain, and as far as we can see we've got something quite remarkable," said Professor Tim Darvill, head of archaeology at Bournemouth University.
"These are the people who built Stonehenge and Avebury - they also signposted their landscape in subtle ways by engraving symbols and images on to rocks."
With his colleague Professor Peter Ucko from London University's Institute of Archaeology, Professor Darvill is leading a research project funded by English Heritage, which will eventually produce a catalogue raisonne of all Britain's rock art.
It will take a long time, perhaps five years, and be expensive - even the six-month pilot study, now under way, to explore what techniques to use will cost pounds 80,000.
But the eventual objective is to create a gazetteer of every design, which will be put on CD-rom and made available to universities, schools, and the public. It is also hoped that computer analysis will allow the meaning of the designs to be understood.
There are about 30 abstract motifs commonly used, the most widely seen being the "cupmark", a teacup-shaped hollow between two and three inches across that is "pecked" - chipped with another stone - into the rock.
Cupmarks may have been used to trap water, and could have represented the sun, moon or stars. The next most common design is the "ring-mark", a spiral set of lines. Between them, these two motifs appear in 70 per cent of designs.
The rest are zigzags and chevron patterns, which some archaeologists think may be representations of a human trance.
"They come in different combinations and there seems to be a `grammar' in the way they've been used," Professor Darvill said. "We will analyse them on computer like you would an early script. My guess is that we will find a patterning, and I hope we get close to an understanding."
His own view is that the motifs are saying something about the landscapes in which they occur. "They seem to be about marking the landscape, perhaps marking ownership, perhaps to mark what kind of things you're coming to.
"Perhaps they tell you what's going on in a valley - if it was a secret valley, a burial area. Maybe you're going into a grazing area, as if they were signposts to what's going on, `Camp here!' That sort of thing."