THE BROADER PICTURE; CAVERNS MEASURELESS TO MAN

In that remote region where the Great Wall of China finally peters out, between the snow-capped Danghe Nanshan mountains and the Gobi desert, one of the great artistic wonders of the world is quietly crumbling away.

The caves of Dunhuang contain treasures every bit as breathtaking as those in the current Mysteries of Ancient China exhibition at the British Museum. Yet they are, for the most part, little-known in the West. A network of some 500 man-made grottoes, hidden inside a cliff-face near the Mongolian border, the caves are a repository for some of the most magnificent flowerings of Chinese culture, collected over a period of 1,000 years. They were originally created as Buddhist shrines, but, from the fifth to the 14th century AD, pilgrims travelling along the Silk Road would come here to record their lives, loves and aspirations in murals and statues.

At different times, the area was under Tibetan and Chinese rule, and the multiplicity of influences reflects the importance of the Silk Road - which passes right by Dunhuang - as an agent of cultural cross-fertilisation. (The meditation hall shown above has images of Hindu deities on the wall behind the statue of Buddha, and one of the two kings mourning the death of Buddha in the main picture was probably from India.)

The murals cover some 45,000 square metres of wall space - about five times the combined area of all the paintings in the Tate and the National Gallery. There are hundreds of thousands of images and scenes, covering every aspect of Chinese life, and about 2,000 clay statues. Simply as a social document, they are unparalleled; but those lucky enough to have entered the caves seem unanimous that they contain art of the highest order.

European interest in Dunhuang has been hampered by its sheer remoteness - 1,300 miles west of Peking. Today, however, a steadily increasing trickle of tourism is combining with other forces of erosion to threaten the very survival of the treasures. Wind, rain, sand erosion and general human activity are all contributing to a slow wearing process. The desert wind blows 2,000 tonnes of sand over the cliff every year, covering the paintings with a layer of potentially abrasive dust. It is also feared that the cliff itself is structurally unstable.

Now scientists from China, Japan and America are collaborating in a complex campaign to hold back the forces of time and nature. Automatic data collection stations record the site's temperature, humidity, wind speed, sunlight, rainfall and carbon dioxide levels. There is a special geological programme to monitor cracks in the cliff-face itself. A textile wind-break more than two miles long (gradually being replaced by a permanent line of desert trees and shrubs) has reduced the sand threat by 60 per cent. And experimental filters installed at the entrances of some caves suggest that dust deposits on the murals could be significantly cut as well.

The delicate medieval paint pigments on the murals are constantly monitored for changes of colour - which might be expected to result from the increased levels of light, humidity and carbon dioxide that come with tourism. Even the rock itself is being tested, to see if there are any chemicals which might be used to make it more resistant to erosion.

Should all these efforts fail, not quite all will be lost, for a spectacular attempt to preserve Dunhuang's greatest treasures for posterity has recently been completed. Dun-huang: Caves of the Singing Sands, by London University's Professor Roderick Whitfield (Textile and Art Publications), an inspiring and detailed analysis of the murals, contains 400 pictures by Japanese photographer Seigo Otsuka. Would-be readers may gasp at the price: pounds 315. They would gasp a lot more if they saw the caves themselves. !