Paul Barker: Bombs may kill and buildings may fall, but the modern city and its citizens prevail

The Spirit of the City: The strength of the modern metropolis; lessons of Manchester and the IRA, 9/11 in New York, Islamist attacks in Paris and Madrid; shock but no panic in London; cities' capacity to survive and recover

For all their strength and the cunning of their citizenry, the old cities did not always survive. Troy was destroyed. So was Carthage. The Aztec capital Tenochtitlan is buried beneath the clamorous roads of today's Mexico City. In Xanadu did Kubla Khan a stately pleasure-dome decree; but there is no more Xanadu, only Beijing, working as fast as it can towards the condition of the modern capitalist city. And such cities -London, New York, Paris, Madrid, for example - are much, much harder to destroy.

For cities themselves have evolved. The bombs last week in London followed the 9/11 attack on New York. But they were preceded by bombs in Madrid commuter trains and, earlier, in the Paris Metro. These onslaughts have demonstrated the strength of the modern city. London, New York and their counterparts will emphatically not go the way of Carthage or Xanadu. They are much tougher cookies than those semi-barbaric creations.

The people who are attacking them don't appear to know, or perhaps care, how such great modern cities work. These have often been portrayed as fragile, heartless creations. The startling images in Fritz Lang's 1926 movie Metropolis embody this hostile view. But the modern city's grey surface of anonymity conceals a hidden resilience. People have chosen to live in a city such as London in pursuit of a cluster of aspirations. They are not going to throw their hand in.

Under threat, the people of London and other modern cities hang together without vociferousness, but united in a refusal to be beaten. They are not going to have the life they have chosen snatched away from them. This is their coherence, their spirit of community. In London's parks yesterday, in the afternoon sunshine, children rolled on the grass, picnics were eaten, grandparents sat on benches feeding the ducks. This was their answer to terror. A city in panic it wasn't.

The great German sociologist Max Weber asserted that, in the fullest urban sense, the city "appears as a general phenomenon only in the west". By contrast, the city of the east, he argued, was a sprawling conglomerate of special interests, with no real coherence. The new anti-urban attackers are inspired by leaders to whom the modern city is either an unknown quantity, or something they abhor as the devil's work. If fellow Muslims are killed in the attacks, too bad: they should not have chosen the evil metropolitan life. The holy cause, they aver, is greater than that.

But such theocratic causes are not greater than the modern city, built on the rock of self-interest and mutual aid. The social ties that bind a city together do not easily snap. The 9/11 atrocity made New Yorkers shudder, but they did not go under.

The very model of a modern city was Manchester. The moment it sprang up as an industrial phenomenon - leaving far behind its origins as a modest market town - it was widely recognised as something completely new. Friedrich Engels went there in order to keep his good friend, Karl Marx, up to date on how the new city was evolving. The great German neo-classical architect, Karl Friedrich Schinkel, also visited it, in order to sketch the unprecedented chimneys of the cotton mills. The long-term solidity of this urban creation was underlined when, in 1996, in one of their last mainland attacks, the IRA planted a bomb in the Manchester city centre. The Royal Exchange Theatre leapt an inch or so into the air, but was soon restored. All around, the city set about healing itself, as it had also done after the blitzing of docks, factories and warehouses in the second world war. Manchester was not defeated. Nor will London be.

Historically, the new kind of city led to new ways of living together, and new forms of politics. In Britain the modern system of political parties was invented in the late 19th century in another adventurous city, Birmingham. Anonymity and organisation go together. The old ties of clan and cult are weakened. After the clammy closeness of village life, millions have taken to their heels and opted for the city. The city is a symbol of aspiration; the country is a symbol of stasis. You are paid your money and you takes your choice.

Where Manchester led, London followed. But some older cities took time to evolve into the fully-fledged modern form. In 1940, Paris knew it would fall to the invading German armies. Streets and houses emptied. Almost everyone had a parent, an aunt, or a great-uncle by marriage, who lived on the family farm somewhere, or else in a little market town. The Parisians at that date, devoted as they were to their city, had another "home" to go to. This would hardly be true of the 21st-century city, stretching out for miles beyond the périphérique road in every direction. Bombs on the Metro were just one incident in a long, resilient history.

Madrid was for years a rather dismal creation of the Spanish royal family, a jumped-up village, a tin-pot capital, chosen to offset the claims of other, longer-established cities. Franco, who became dictator in 1939 after winning a vicious civil war, changed all that. Helped by his henchmen in the Roman Catholic freemasonry of Opus Dei, he drove Madrid into a new status as a modern city, investing in it and expanding it. This was the city the train terrorists unsuccessfully tried to destroy; by now it was the headquarters of a flourishing democracy.

The terrorists will fail in London, also. The modern metropolis is a tight and complex knot. Cut one string, and the other loops and turns will still stand fast. Civilisation and barbarism will always fight each other. But civilisation, as embodied in great cities like London, is winning the evolutionary battle.

Paul Barker is a senior research fellow of the Young Foundation, formerly the Institute of Community Studies