Outrage.

Machu Picchu is being unbuilt - though no one knows exactly what it was like before being laid waste by earthquake and jungle. Rebuilding blurs the image and prevents proper archaelogical research. It should stop at least until we understand more.

Machu Picchu is one of the world's most famous places, made the more romantic by being discovered by the American archaeologist Hiram Bingham in the jungles of the upper Amazon basin barely 90 years ago. It is one of the most sublime sites in the world in the sense that Edmund Burke defined: while Beauty is the aesthetic appreciation of the sense of self procreation, the Sublime is the equivalent for self preservation. Quite quickly, it becomes apparent that Machu Picchu is threatening, as you climb up an apparently interminable staircase from the mini-bus entrance to the high place that commands a view of the whole. After a while, every step is painful because of lack of oxygen. Though you are only 2500m high (8000ft), your heart races; your mouth is dry from gasping; your lungs are not big enough to accommodate enough hot wet tropical air. Death is in the atmosphere as you look down, the more so because the famous site hovers over a U-bend in the river Urubamba, with terrifying vertiginous precipices on all sides.

A plateau is enclosed by buildings and a peak (Huayna Picchu that commands the end of the U), and is surrounded by higher green-jungle mountains. In a sense Machu Picchu is a very large castle, with defensive works and a large self-sustaining agricultural system. The Spanish apparently never got there (though the bones of a horse - the equivalent of the conquerors' battle tank) have been found.

Because the Incas did not write, and the Spanish were totally indifferent to the native culture - apart of course from gold and silver of the mines - no one really knows what Machu Picchu was for. But endless theories have been produced. Bingham thought that he had found the lost city of Vilcabamba, the legendary place from where the last vestiges of Inca culture resisted the Hispanic. So far as can be determined by more recent discoveries, it was a fastness, a settlement devoted to religion, power, creation and storage of resources, part of a network of such (some perhaps still undiscovered), serving the capital Cusco, 1000m (3000ft) higher up on a high plateau of the Andes. It was one of the chief centres of the Incas' amazingly integrated economic system that relied on food production, distribution and storage to make an empire stretching from territories as far apart as modern Argentina and Ecuador. Most of the graves at Machu Picchu are of women: the men were either fighting each other or the Spanish. C atastrophic epidemics of European diseases coming down from Mexico, in advance of the conquistadors, destroyed much of the Incas' ability to resist. Numerous fragments of construction show that the place was far from finished when it was overwhelmed by the jungle.

It is being rebuilt. Above the fabled and astonishingly precise Inca masonry of the base levels, upper parts were probably made of random rubble skimmed with render. But no one knows how they were done. Their stones are being replaced without clear direction. No serious or detailed archaeological investigation of the site has been published since the middle of the last century, though very many advances have been made in the discipline.

Instead, money is being put into making a hypothetical reconstruction, which will prevent proper analysis of the past. The threat of a cable car terminal being blasted Out of the mountain near the stultifyingly banal tourist hotel that dominates approach is, thank goodness, averted. (Though a better aerial solution could be achievable.) But, however impoverished Peru may be, and however necessary tourist dollars, it is totally wrong to make fabular reconstructions of a World Heritage site, one equal to the Taj Mahal or Stonehenge. UNESCO must help find the will (and money) to enable us to understand Machu Picchu with new research, rather than allowing the fabulous citadel to drip into smearily blurred Disneyesque pastiche.