Toulouse is no ordinary French provincial city. Nicholas Lezard finds the atmosphere a little grungy, a little corrupt - but he feels at home

I am suspicious of cities that are full of construction sites. This is not necessarily a good suspicion to have; after all, cities need to keep changing. An artist can say of his statue that it is finished, but if one says the same of a city it means something far worse. But when a city as ancient as Toulouse makes such a racket in rebuilding itself, you can't help smelling a rat.

I am suspicious of cities that are full of construction sites. This is not necessarily a good suspicion to have; after all, cities need to keep changing. An artist can say of his statue that it is finished, but if one says the same of a city it means something far worse. But when a city as ancient as Toulouse makes such a racket in rebuilding itself, you can't help smelling a rat.

Sometimes reconstruction is unavoidable in what is an old city: friends living in a surprisingly common-or-garden 13th-century building, in a relatively undistinguished area, had to move out when the walls fell down. Nearer the centre, however, the Marché Victor Hugo, which looks as if it was hurriedly designed on a napkin in 1968, is already being rebuilt. Rebuilt, it seems, disconcertingly, to look exactly the same as it did before.

The pavements, often so narrow they are more like running boards on a vintage car than anything you can walk two abreast on (and never mind push a child's buggy along), vanish altogether and you have to step into the street, protected, if that is the word, from the traffic by fragile-looking wire cages. If you have small children, you spend a lot of time keeping an eye on them.

So the air is full of the silicate tang of masonry dust (that chill draught you feel and smell when you walk past a house being done up), the whine of concrete saws and chugga-chugga of drills. To what purpose, you ask yourself. In the case of the Place Arnaud-Bernard, a rather funky open space with Algerian and Moroccan cafés and the like, the purpose is clearly to stop the North Africans and the SDFs - the sans domiciles fixés, or homeless - from having a place to hang out visibly. This does not stop the SDFs from virtually lining the adjacent Boulevard d'Arcole.

The Mayor of Toulouse, Dominique Baudis, is a right-wing ex-journalist and local historian, making one wonder who the London equivalent would be - Paul Johnson instead of Ken Livingstone, perhaps. Mr Baudis is already into his second term, but any clean-up of the city that has arisen from his electoral success cannot even be said to be cosmetic.

As ever in France, culture and counter-culture rub up against each other, but pretend the other is not there. Semi-official A3 flyers advertising a " rencontre au graffiti" abounded on my visit; this, presumably, was an attempt to seduce the more tolerant of the bourgeoisie to the semiotics and artistic ethos behind graffiti, but it struck me that no arranged event was necessary: you meet graffiti everywhere you go. Toulouse is the most scribbled-on city I have ever seen, and there are plenty of contenders for that title. Gallic tolerance towards this habit seems to have been taken a little far, and if Toulousains think it gives their city a hip and vibrant edge, then they are kidding themselves.

That Mr Baudis, whose other big idea is a metro line that hardly goes anywhere, seems more interested in making life difficult for Algerians and street theatre troupes than stopping his city from looking like a particularly delinquent teenager's bedroom, is itself deeply depressing. But Toulousains are an extraordinarily civil and good-natured bunch, not to mention possessors of an extraordinary high incidence of natural beauty.

Banish all thought of snooty Parisians, themselves not as numerous as legend proclaims; enjoy what really seems like genuine thanks from shops you have visited - in inverse proportion to the price of the goods sold, of course. Even the local grocer, with his arresting variation on the "no credit" sign above the till (" Le credit est mort: les mauvais payeurs l'ont tué" - Credit is dead: bad payers killed it) was infallibly polite, even when none of my credit cards worked. The pony-tailed head waiter at Chez Emil on the Place St George may have been a little too cheeky, considering how long we had had to wait for our menus, never mind our food, to arrive: but then he knew he was working for one of the city's most popular restaurants.

Toulousains make much of their city's beauty, its ancient churches, its lovely pink colour, even as it lies about the place in rubble or is spray-canned by yahoos. "O Toulouse", said one striking graffito, and we presume the tone was one of rapture as opposed to exasperation. Well, beauty being in the eye of the beholder, I find the more striking architecture of the place gives me the willies in a way nowhere else has.

Take the church of the Jacobins, Thomas Aquinas's last resting place: it is the most frightening building I have ever seen. A speculative mapper, among other things, of the punishments of hell, it is fitting that there should be so much about it that seems infernal. "It looks like a ship", is how the locals generally describe it; yes, fine, a ship, then, but not one you would ever want to sail in.

Immensely, even disproportionately tall, the church towers above you like a titan's prison. Like most of the rest of Toulouse that is not made of concrete or under wraps, it is made of the ubiquitous red-pink brick, in reality a slab whose default dimensions are about 16in by 12in by 2in. I could not begin to compute how many went into the making of the Jacobins, but the edifice bespeaks an exorbitant, maniacal and despotic architecture: millions of these bricks are piled on top of each other, singing, wildly and mournfully, of the immense labour and pain that must have gone into their laying. Their very colour suggests that they were fired in no earthly oven, steeped in the blood of the Cathars the town massacred eight centuries ago, heretics it seems pointless to have persecuted so ruthlessly, given that they held procreation a sin, and so were never going to last more than a generation or two.

At the top, in the far distance as you crane your head back to examine them, twisted gargoyles jut out, looking as though they have been frozen in the middle of being tortured in hell: they are the most human element of the entire building. (You can see their relatives, life-size and upended in the cloisters of the Musée des Augustins; close up they look almost tame, and you can pose your naughty children pulling gargoyle faces in between them for a quick snap.)

The interior is just as stark, nude of almost all ornament. Apart from Aquinas's modest tomb and what looks like a startlingly makeshift altar, there is nothing inside but space, and the ghosts of ancient murals and friezes, presumably erased in an earlier, more successful anti-graffiti drive.

There are a few inane Madonnas dotted about in alcoves, but they hardly even attain the level of the ludicrous, looking as though they have been put there until something better shows up in some religious flea market.

The columns reach up and spread their huge stone tentacles across the impossibly high vault; the space itself resonates with a low, murmuring hum, like the faint background moan of ancient souls suffering in the afterlife. It is so spooky that even children are silenced. There are soothing cloisters beyond, but on the day we went they were closed for the shooting of some stupid French film about D'Artagnan, upon whose cast, crew and most specifically location manager I pronounced a heartfelt curse.

There is something of ancient corruption about the city: its wealth and international status was founded on the pastel, a vegetable dye that made a number of families so powerful and rich that their names still crop up all over the city.

Perhaps it was this, on top of a sensitivity to architecture I never suspected I possessed, that made me say to myself, four years ago, that I'd never set foot in the place again. Sometimes, however, you just have to; besides, it really is a nice place, and it is better to be terrified by a building than not to feel anything about it at all.

The famous Toulousain diet - duck, and duck by-products, basically - might look on paper as a recipe for cardiac seizure, but it produces among the longest-lived inhabitants of Europe, and perhaps, as well, their general sense of well-being. A 13th-century rhyme names it as the original land of Cockaigne, " qui plus y dort plus y gaigne"; you made money while you slept.

Toulouse is grungy but beautiful, lazy but industrious, alluring and terrifying, sybaritic and healthy. We spent our time wondering why we wouldn't want to live there, and couldn't really come up with any serious reasons.