Why didn't Britain build like Paris or Rome?

After London, of course, the first major world city I ever visited was Paris. Aged 20, I was already primed with the memoirs of artists and writers - such as Hemingway and Fitzgerald, James Joyce and Gertrude Stein, Oscar Wilde and

William Rothenstein - so much of the city's public life, its cafes, markets and restaurants, came as no surprise. What was a constant unexpected exhilaration was its scale and grandeur. How did Paris get like this and why did London not?

Since the 17th century London has been, and remains by far, the largest city in Europe, yet for the former capital of a world empire it appears strikingly unmonumental and unplanned. In Paris, by contrast, every Haussmann boulevard offered a grand sweep to a splendid rhetorical climax. A great axis runs for several miles from the great pillar at Bastille in the east, by way of the rue de Rivoli, the massive palace of the Louvre, the gardens of the Tuileries, the Place de la Concorde, the Champs-Elysées, to the terrifying roundabout at Etoile crowned with the tricolour-bedecked Arc de Triomphe and on and on ... to the clutch of Modernist and Post-Modernist skyscrapers at La Défense, where La Grande Arche, at a slight ironic angle, ends the progress and looks out on the dystopian housing estates of the banlieues. The Mall in central London with the undistinguished Buckingham Palace at one end and the dog's dinner of Trafalgar Square at the other is scarcely in competition.

Our very different histories brought us here. The unification of France into a nation-state created a strong centralised absolute monarchy, notably in the long reign of Louis XIV, which diminished the rival powers of the aristocracy and commanded all the arts, including architecture, to serve the country's prestige and express its values. To a remarkable extent, two monarchies, two empires and five republics later, this policy continues; much of French cultural life is still funded by the government and les grands projets ordered by President Mitterrand - the Pyramid in the Louvre, the Bastille Opera, the Bibliotèque Nationale - follow the path from Versailles and the creation there of the Sun King.

Most of us in this country - and anyone who has ever had to deal with French bureaucracy - would probably be willing to forego such architectural grandeur in return for our own less intrusive state and our liberties under law. After the Great Fire of London in 1666, the capital had the unique opportunity to solve its chronic problems of overcrowding and traffic congestion and choose one of the many plans, Christopher Wren's among them, for a city of wide boulevards and grand piazzas. But it didn't - not least because of the expense of litigation and compensation for all those whose property rights would be ridden over roughshod by such grandiose designs. St Paul's was rebuilt, to become the greatest architectural monument in the capital, but with insufficient space around it to make it a wonder on a par with St Peter's in Rome (with the Coliseum, the Pantheon, the Baths of Caracalla and the Vatican it's the hometown of megalomaniac architecture). The Blitz cleared the space once more, but the mercantile classes crowded in again, too greedy and too sensible to be splendid.

V S Pritchett, in his essay "London Perceived", observed that "dictators can be splendid, democracies can swagger, but parliaments cannot bear the expense". Autocracies are obviously a good thing if you're in the construction business - there's just the one client to deal with, they think big, and obviously the peasants are going to pay for the whole thing if not actually build it. A quick look around Europe brings up several fine examples. Above all, St Petersburg, Peter the Great's titanic enterprise to build a metropolis to rival Paris or Venice on a swamp near the mouth of the Neva. His Winter Palace, which now houses the Hermitage, one of the world's finest art collections, has more than 10 kilometres of halls and corridors. (Aleksandr Sokurov's 2002 film about the Hermitage and its history, Russian Ark, matched its scale by using more than 2,000 actors and three live orchestras in one single, continuous 90-minute take.)

Vienna was already one of the largest cities in Europe when its emperor Franz Josef demolished its walls and defences in the middle of the 19th century to create a vast boulevard encircling the oldest parts, including the cathedral and imperial palace, and providing space for a series of enormous buildings, including the Opera House, the Kunsthistorisches Museum, the Parliament and University.

Berlin too, as Prussia struggled to come out top of the German states and statelets in the course of the 19th century, assembled a dramatic collection of architecture - among them, the Brandenburg Gate on the east-west axis of Unter den Linden, and Schinkel's vast neo-classical Altes Museum.

After the German Empire was proclaimed in 1871, imperial tastes turned rather bombastic, but Schinkel's pupils ensured that his Altes Museum was joined on its island in the Spree by equally elegant, but massive buildings, including the Pergamon Museum, housing the city's superb archaeological collection.

And "democracies can swagger". In the past 150 years much of the most impressive architecture has been in service of traffic. On my first visit to New York, what impressed me most were not the behemoth skyscrapers of mid and downtown Manhattan, but the colossal size and ambition of the Brooklyn Bridge (completed 1883) and of Grand Central Station (1913 - now sadly reduced to running commuter trains only. Its destination boards are worthy of carrying "Beijing", "Ulan Bator" and "Samarkand".)

At least in such engineering triumphs Britain can compete: our Rail and Road Bridges over the Firth of Forth and Brunel's Clifton Suspension Bridge show that, in the great age of construction, our modest and consensual civil society did not prevent such heroic works of the architectural imagination.