"To have built in heaven high towers"

The tower is a symbol of strength, of power, of ambition. Not for nothing does Milton make his fallen angel Mulciber a tower-builder. A tower isn't just a fortress; it's a statement, a claim to attention.

Look at the late medieval Italian cityscape and you'll see it's full of assertive towers, like the Torre dei Guinigi in Lucca - fortresses for the feuding noble families of the independent city state. San Gimignano and Bologna bristle with towers like spines on a porcupine.

Look at the English Perpendicular church and you'll see the loftiness and aspiration of the tower used for the greater glory of God - and the glory, too, of those wealthy families which contributed to the building work. East Anglia is full of fine flint-built towers, with stone used to pick out the details; and Somerset, another wealthy area in the late middle ages, possesses marvellously ornate stone towers festooned with arcading, niches, turrets and pinnacles.

I thought of all this today when I read about Jean Nouvel's plans for a new tower in La Defense, Paris. The area is currently an office ghetto - busy by day, deserted at night - but there are plans to create more residential and services buildings. All of which could, of course, be done without a tower; but the tower is the icon, the symbol which encapsulates the city-changing ambition of the plan.

La Defense is not actually in Paris. It's in Hauts-de-Seine departement. Any development here will drain residents, jobs and taxes away from central Paris - whose 20 arrondissements are governed by Bertrand Delanoe, mayor of Paris.

So Delanoe has his own plans for a 'mini-Manhattan' of towers to regenerate the poorer east and north areas of central Paris. (Incidentally, are all cities the same - richer on the south and west, poorer on east and north? London certainly fits this schema. So does Berlin, I think - though that might be for different reasons.)

The same effect could surely be gained by high density building six or seven storeys high - which is what gives the centre of 19th century Paris its particular character. But no, it has to be towers - in a strident last burst of phallicism, towers are becoming the twenty-first century city's sine qua non.

But we've seen all this before. Back in the 1960s towers were the thing - and the sleep of reason produced monsters; the Tour Montparnasse, much hated by Parisians, and Centre Point, the greatest white elephant in London. (The French joke about Belgians being stupid, and retail the story of the Belgian terrorist who blew up the Tour Montparnasse - the joke being that if he ever did so, he'd become a French national hero overnight!)

It all reminds me of that 1980s battle between the City of London and Canary Wharf, an unseemly squabble between traditionalists and modernisers that saw petty local interest as more important than the ultimate fture of London as a financial centre. And that battle too saw the aggressive young upstarts building towers - the Cesare Pelli tower at Canary Wharf, at first standing in splendid isolation, then joined by others as the area began to thrive.

And that's the real sadness of towers. The more there are, the less the effect.

There's a place where the M11 comes over the brow of a hill and starts to descend into the Thames Valley, and you used to look ahead and see that one proud tower standing on its own. At dusk, with the lights on inside and a red aircraft warning light twinkling on the top, and the grey of the landscape misty beyond it, it was a view like no other.

And now it's just crowded into a forest of skyscrapers. It's lost what made it special.

"And so the whirliig of time brings about its revenges." Now, it's the City that is building the towers. The Gherkin, the Shard of Glass, the Cheesegrater, the Walkie-Talkie - towers that have entered the vernacular even before most of them have been built. The traditionalist financiers have turned avant-garde developers, learning from Canary Wharf.