Firminy is a small, industrial town, part old, part modern, in a bowl of beautiful, wooded hills on the edge of the Massif Central. You might easily be in the Pennines or in the valleys of south Wales. On the high street in the older part of town, loudspeakers broadcast merry, seasonal music, including "White Christmas" and "Jingle Bells" in French. This might seem like an odd place to seek the blueprint for a contented, urban future for mankind. Look again.
In the new year, one district of the town of Firminy is likely to be declared a world heritage site by Unesco, joining a list which includes the banks of the river Seine in Paris, the lagoon and canals of Venice and the Tower of London. The coal mines on which Firminy's prosperity was originally built closed down in the 1930s. Engineering has prospered and slumped. Now the town believes that it may be sitting on a mine of long- neglected, tourist gold: the largest concentration of buildings in Europe designed by the most influential, the most admired - and the most detested - architect of the 20th century.
His name was Le Corbusier. He died in a swimming accident in 1965, aged 78.
Forty one years after his death, Firminy has just completed one of Le Corbusier's final designs: a stunning, concrete church which looks like a giant ship's funnel or a vast, upturned ice-cream cone, with the point broken off. Work on the church, abandoned in 1978, has been finished with the help of one of Le Corbusier's pupils. It completes - or almost completes - an ensemble of buildings which forms the largest Le Corbusier urban landscape in Europe. The only larger collection in the world is in the "new" town of Chandigarh in India.
Le Corbusier was, among other things, the apostle of concrete, the artist of high-rise. To his critics, he is the father, or grandfather, of a million charmless tower blocks, sink estates, shopping centres and multi-storey car parks. One architectural writer has even suggested that Le Corbusier - real name Charles Êdouard Jeanneret Gris - was "evil".
To his admirers, the Franco-Swiss architect is a traduced genius, a man whose ideas might have offered - and might still offer - a vision of civilised urban living for poor and rich alike.
It was announced this month that more than half the world's population of 6,673,300,000 has now squashed into cities (with millions more on their way). Le Corbusier's defenders say his ideas, intended to make the city of the future more human, are as relevant and vital as ever.
In the new year, France - joined by Belgium, Germany and Argentina - is expected to propose that the whole of Le Corbusier's work, about 130 buildings worldwide, should be declared a world heritage site by the UN cultural body, Unesco. No other architect has been honoured in this way.
Le Corbusier spoke of his building as "machines for living": His critics have stressed the word "machine"; Le Corbusier stressed the "living". He saw his approach as a way of using the "machine" - modern materials and engineering techniques - to free ordinary people from the airless, light-deficient, cramped, damp slums of the 19th century.
He seized on the idea of the tower block as a way of providing, at reasonable expense, spacious, peaceful, light-filled homes for the masses. By building upwards, space would be liberated to surround such buildings with gardens and sports and cultural facilities.
Le Corbusier's idea was that such districts should be built within or alongside the historic centres of existing cities. Many of the normal amenities of the street - shops, schools, restaurants, cafés, social centres - would be incorporated into streets within the tower blocks themselves.
Le Corbusier adopted this approach in one of his most celebrated designs, the 12-storey, "Unité d'habitation" in Marseilles, built in 1952. The tower - now a much sought-after address - houses 1,600 people. The block, originally called La Cité Radieuse, or the "radiant city", includes floors for shopping, social clubs, child care, a gym and a hotel. There is a rooftop garden and swimming pool.
A smaller, less elaborate version is part of the collection of Le Corbusier buildings in Firminy. This baby "unité" - which has a school and social meeting rooms - is still 60 per cent occupied by council tenants. It is said by its residents to be a model of harmony and neighbourliness.
Both buildings look at first glance like the dreary, tombstone tower blocks that followed in almost in every town and city and council estate in the world. The resemblance ends there. Most of these imitations, from Chicago to Clichy-sous-Bois, by way of Tottenham and Wythenshawe, were cheaply built, with dark, cramped apartments separated by paper-thin walls. They were marooned far from town centres. They had few local facilities and certainly no internal shops and streets. Roof-top swimming pools were scarce.
Such buildings have become synonymous with the "this-will-do" school of architecture of the 1970s and 1980s. They have become indelibly associated with social alienation, deprivation and youth violence. One French commentator even blamed Le Corbusier for the suburban riots in France last year.
Yvan Mettaud, curator of the Le Corbusier buildings in Firminy and an expert on the architect, said: "Le Corbusier is blamed because he is the name people know. But he is attacked for what others perpetrated, which was utterly against the spirit of his ideas. Instead, we should blame the politics, the money driven politics, the antisocial politics, which built so many hundreds of shoddy structures without facilities in new areas far away from town centres."
The importance of the Le Corbusier-inspired district of Firminy, M. Mettaud says, is that it provides a glimpse of what might have been. On the edge of the old town - in Firminy Vert, or "green Firminy" - there are a half-dozen blocks of flats, designed by Le Corbusier or his pupils. Beside them is a startlingly beautiful, concrete sports stadium, a striking cultural centre in the shape of an elongated wedge, a swimming pool and now a church.
The original design of some of the blocks of flats was tampered with in the 1980s. The cultural centre has been cruelly neglected for decades and - beautiful shape apart - it now has the miserable, dark-grey, concrete look of a motorway flyover. The town and region, and the metropolitan area of Saint Etienne, plan to correct this neglect as part of the next phase of restoration work.
All the same, the Le Corbusier approach - though incomplete and though badly maintained for years - seems to have worked. In November of last year, there were riots and car-burnings in almost every town and city in France. Firminy, a relatively poor, multiracial town with high unemployment, was one of a handful of towns where not a single car was burnt.
No one suggests that Le Corbusier should receive all the credit. Firminy is a well-run town. But M. Mettaud says the fact that the new parts of Firminy incorporate beauty and spaces for cultural and sporting activity has its effect on social behaviour.
"Good architecture cannot force people to live together in harmony. Bad architecture can certainly prevent them from doing so. The Le Corbusier approach does not create social harmony. But it does enable it and encourage it," he added.
Le Corbusier's more subtle critics accept that he had a "humanist" vision of the city of the future, but they suggest that he was too abstract and too sweeping in his rejection of the past. One of his pet schemes - never taken seriously, like many of his plans - was to knock down much of the right bank of Paris and replace it with gardens and freeways surrounding neat rows of "unités d'habitation".
Le Corbusier was guilty, say his critics, of a form of architectural totalitarianism. His humanist vision, like other would-be humanist visions of the 20th century, became inhuman. It tried to impose too uniform and clean a mould on the complexity and irregularity of human nature.
And yet there is nothing uniform or regular about Le Corbusier's best buildings, which must now be extended to include the recently finished church of Saint Pierre in Firminy.
A visionary mayor of the town, Eugene Claudius-Petit, invited Le Corbusier to experiment with a derelict industrial site on the edge of the town centre in the 1950s. The stadium and cultural centre, and one of the three "unités" originally planned, were completed before or just after his death. Construction of the church began six years later, in 1971. Mayor Claudius-Petit was defeated in a municipal election in 1978. The Communist mayors who followed him halted all work on Firminy Vert.
The stump of the unfinished church was almost demolished, but was rescued by state protection orders in 1987 and 1995. The very existence of Firminy Vert - although known to Le Corbusier fans - was much less well known to the modernist-minded tourist public. In 2001, a new centre-right mayor, Dino Cineri, was elected.
"I was brought up in one of the blocks of apartments in Firminy Vert," M. Cineri told The Independent. " Even when I became mayor, I had not fully realised the jewel that we have here. I said to my deputy that we must find some kind of beacon to attract attention to Firminy. He said you don't need to look very far. Hundreds of thousands of tourists from all over the world visit other Le Corbusier sites. We have the second most elaborate Le Corbusier site in the world, the largest in Europe, and it's relatively undiscovered." With backing from the European Union and regional and national governments, and updated designs by Le Corbusier's former pupil, José Oubrerie, work on the church resumed after 28 years and was completed this month. The main auditorium - to be used for cultural events as well as church services - is a soaring concrete cavern or cathedral. Natural light pours in through angled, coloured strips and holes in the walls, recreating the effect of stained glass in a cathedral. The ground slopes asymmetrically, recalling the floor of a natural cavern. The rooms below, which are to become a modern art museum and Le Corbusier visitor centre, are less impressive. The raw concrete walls have the rough, depressing feel of a multi-storey car park.
Is that not one of the problems with Le Corbusier? His style depends on concrete and concrete is an unforgiving material, especially when it ages. M. Mettaud disagrees: "There is nothing wrong with concrete in itself," he said. "I love concrete. I like to stroke its smoothness. Concrete is just another form of stone. It can age as gracefully as stone, if it is well maintained. Unfortunately, it is often treated as a cheap material, which invites neglect. Even a little bit of cleaning each year with soap and water makes a vast difference."
Not every convinced anti-modernist will be converted by a visit to Firminy. Firminy Vert is relatively small. The rest of the town is littered with other modern buildings which share the typically dreary, post-Le Corbusier faults of the 1970s and 1980s.
All the same, there is something pleasant and reassuringly gentle about the Le Corbusier site. The town hopes that many thousands of architecture students and tourists will come to Firminy to consider what might have been. And what might still yet be.
M. Mettaud said: "Le Corbusier's ideas were mostly rejected or corrupted by the 20th century. Cities all over the world are struggling to cope with explosions of population. Who is to say that Le Corbusier's time might not come in the 21st century, or the 22nd?"
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