Time frame.

Matera, an almost forgotten town in southern Italy, is a marvellous collage of civilisation from neolithic times to the last century. UNESCO has listed it a monument in danger, but is it too late?

In 1994, UNESCO put the ancient southern Italian town of Matera on a shortlist of monuments in urgent need of restoration. Since that is all that has happened, the gesture seems to have been more symbolic than otherwise, but the intention may simply have been to bring an extraordinary place to the world's attention. Apart from a handful of inhabitants, Matera is a ghost town, situated between Calabria and Puglia in a stony landscape forming part of the ancient hills of the Murge, a rough limestone region of volcanic origin. The town was originally troglodytic, spreading densely as if it were one organic body over the slopes of a hill, built into its cavities and out of the surrounding limestone. More or less deserted for 30 years, long neglected and, until the UNESCO initiative, almost unknown outside Italy, the town is melting back by degrees into the landscape.

In Italy, Matera's neglect has long been viewed with concern, for few places contain so concentrated a record of man's passage from neolithic to modern times. Matera embodies in miniature a clear set of cultural intersections between the palaeolithic and the first and second millennia, between east and west, and between the sacred and profane. The archaeological riches of the site are overwhelming. The limestone is honeycombed with natural caves and underground passages where abundant traces of neolithic man's activity have been found.

Today, the town belongs to the Basilicata, a region known in Roman times as Lucania. The name Matera comes from Matheolae, the Latin name for the place. This, in turn, seems to have been a corruption of the Greek name, Mateos Olos, which signifies a 'place devoid of substance', and is a metaphor for the city of caverns and indication of a Greek past, the physical imprint of which can be discerned.

From the fifth century onwards, the caverns were repositories of strong religious zeal. Persecuted Byzantine monks took refuge here and within a few centuries turned Matera into a radiant Christian centre of ascetic and missionary vision. The phenomenon which lasted for more than a millennium was an important source of the rich artistic heritage distributed among the many of the city's cells. The frescoes that cover their walls are in a sad state of preservation, but though fragmented and fading are nonetheless precious and thrilling.

Matera offers eloquent illustration of religious transition that occurred during the Middle Ages within the Christian faith from Constantinople to Rome, for their legacies coexist, often within the same modest space. In one of the lower subterranean rooms a fine Renaissance fresco unfurls itself beneath a vault decorated with a Byzantine cross.

The monks conferred dignity on cave dwelling, attracting other more secular inhabitants. They began to carve dwellings (called sassi in Italian) for themselves out of the huge stone outcrops of the hill face. Little by little, the dwellings were extended outwards so that the roof of one dwelling became in ziggurat fashion the terrace of the one above; and gradually a dense and intricate structure emerged.

As Matera's missionary influence began to wane, during the seventeenth century, so its population began to invade the monks' cells, transforming them into family dwellings. Many altar-rooms became kitchens and fine paintings were obliterated by whitewash.

As post-Second World War dwellings, the sassi were romantic but not ideal, being difficult to convert to the conveniences of the twentieth century. The town was used by one politician or another as the archetype of backwardness and insalubrity, serving as a vehicle of self-interest and a useful weapon with which to belabour the opposition. When in the '60s, a dynamic local major suggested a move to a brand new local authority estate on the outskirts, the troglodytes concurred and eventually 60 000 people migrated. Almost none have returned.

What to do with such an extraordinary and moving no-man's-land? There is no easy answer. Converting the dwellings to modern standards is hardly conceivable. Even if this were desirable, resources are scarce, no willing workforce is available and the cost would be huge. However, there is a small community of 400 people artists, architects, writers and craftsmen - who are committed to Matera. Led by an architect, Pietro Laureano, they are working slowly to restore what they can.

Another idea is to keep the town as a museum; but how big a museum should it be? If it is to constitute only the area with the richest remains and the most important urban sequences, more than half the urban tissue must be heft to crumble. The flow of tourists is negligible (fortunately in some ways). Matera is isolated, transport is difficult and summers here are extremely hot and dry. Moreover, Italy's exceptionally rich artistic heritage makes it difficult to plead for money to maintain such a museum, in spite of UNESCO's listing.

But ruin has many charms. Wandering at random in this thrilling labyrinth is an incomparable experience. You can feel the presence of spirits, and you can become acquainted by degree and accidental discovery with a long cross section of Western culture.