The network responsible for bombing three trains in central Madrid on 11 March wants you to think twice before descending into the Underground, boarding a city bus, or strolling down Oxford Street on a Saturday afternoon. But do the Madrid attacks augur a new era of urban anxiety and insecurity, scaring city-dwellers, corporate offices and large retailers out of Europe's metropolises and into the quiet countryside and suburbs? Will terrorism kill great cities, and the long histories of political organisation, cultural imagination and social integration that they embody?

In the immediate aftermath of Spain's tragedy, some European experts worried that an emerging culture of fear over catastrophic violence would end the urban age. For the past three decades, extremist groups - both foreign and domestic - have made periodic, sometimes repeated, assaults on European cities. Great Britain, Germany, Italy, Greece and Spain have endured dozens of deadly attacks, and organisations linked to the Algerian civil war bombed the Paris Metro in 1995, killing eight people and wounding 200. But according to a New York Times headline, published above a dramatic photograph of "a normally packed Madrid subway car" running near-empty on 12 March, "This time it's different".

The threats from networks such as al-Qaeda include biological and chemical weapons, even a nuclear dirty bomb, and are so horrifying that officials are already planning for doomsday scenarios. Major cities, which are prime symbolic targets, are particularly vulnerable. Urban health agencies and emergency responders are updating their disaster management systems and protecting their water supplies; residents are devising escape routes and feeling anxious in their daily routines. The spectre of abandoned capitals - like the London evoked in Danny Boyle's film 28 Days Later, scripted by Alex Garland - is beginning to haunt Europe. These are nervous times.

But it is too early to write off the city.

Consider Manhattan. Countless American pundits predicted that it would go down soon after the twin towers. Who, they asked, would buy or develop property in New York City, let alone around Wall Street, after 11 September? The answer: everyone who can afford it. Property values are way up from 2001, and real estate surrounding the World Trade Center is among the priciest in town. The US may be in a recession, but the New York City market is soaring again.

Remember the death of the skyscraper, which 9/11 would render obsolete? Today, architects are breaking vertical barriers from Shanghai to Chicago and the Freedom Tower (the centrepiece of the new World Trade Center site) is audaciously designed to reach 1,776 feet. The end of irony and urbane sensibilities, now deemed inappropriate for such treacherous times? Please. The comedy series Curb Your Enthusiasm, which is set in LA and makes Seinfeld look earnest, is the darling of TV critics and a smash hit. The end of urban glamour and conspicuous consumption? In January, several of America's top chefs opened new signature restaurants, with dinners priced at roughly $200 per person, in the new AOL Time Warner complex - twin towers, made of glistening teal glass, on the edge of Central Park. The end of big city crowds? Try Times Square on New Year's Eve.

In Spain, too, citizens have already expressed their refusal to give up the city. On 12 March, approximately eight million people - one in every four Spaniards - took to the streets to protest the train bombings. The nation's urban public spaces had never been so crowded, nor so important, as they were that day.

History tells us that cultural and political responses to fears in the city vary dramatically from place to place, however, and it is hard to predict what citizens and officials will do in the name of urban security. In the 18th and 19th centuries, anxious elites in the UK and the US fled their cities and built clean, wholesome suburbs, once factories and the working classes moved into town. In France, however, the affluent stood guard (or at least the planners, developers and armies working for them did) in claiming Paris for themselves while relegating "the dangerous classes" to the outskirts. The metropolitan areas of all three countries bear the marks of these reactions today.

During the cold war, US defence strategists also participated in city planning. In the 1950s and 1960s, urban intellectuals and political officials who worried about nuclear attacks on urban centres advocated population dispersal. Schools, factories and families conducted drills to prepare for the bomb; homeowners built shelters in their basements. But it was fear of blacks, not of bombs, that sent most white, middle-class city-dwellers to the suburbs; and the US government's failure to redress the rising segregation and head off the riots of the 1960s proved more damaging than the cold war to cities in the US.

How will we respond this time around? After 11 September 2001, President Bush's administration engineered an invasion of Afghanistan, curbed civil liberties at home - particularly for Arab Americans - with the Patriot Act and the new Office of Homeland Security, revolutionised US foreign policy by legitimating pre-emptive attacks, and then launched an unpopular war in Iraq, all in the name of protecting Americans and American cities. (Yet according to a poll conducted in February, Americans are evenly split on whether military action in Iraq increased or decreased the threat of terrorism, and about two-thirds of British, Spanish and Italian respondents believe the war increased terrorist threats.) The US government required male immigrants aged 16 or above, entering the US on temporary visas from specified Muslim or Arab countries, to register with the Immigration and Naturalisation Service; it increased surveillance of foreign students; and it detained hundreds of prisoners in Guantanamo Bay, Cuba, without formally charging them with any crimes.

Today, an increasing number of Americans believe that their government went too far. The necessary policy changes - federalising airport security systems; increasing inspections at ports; guarding bridges and tunnels in large cities, for instance - have been overshadowed by the excesses, the deceptions, the abuses of power and privilege that have made Bush less popular than he was before 9/11. Most European leaders do not need Bush's example to know that the emerging threats to their nations, and the rising fear in them, warrant a different kind of response.

But that does not mean the culture of fear will not fundamentally alter Europe's urban landscape. Indeed, it already has. But since the 1980s, the sources of most urban anxiety have not been terrorists, but stigmatised ethnic and racial minorities, immigrants, criminals, drug-users and the poor. Following the US model, in which surveillance and punishment are the preferred methods of social regulation, European cities have expanded their police forces and toughened penalties, resulting in dramatically increased rates of incarceration across the Continent. New anxieties will accelerate this trend, but with a twist: Arabs and North Africans will be subjected to heightened ethnic or racial profiling, and citizens will begin monitoring each other more aggressively.

Contemporary urban architecture is already designed for this climate of fear - indeed, it encourages it. Gated communities, streetside video cameras, home alarm systems and private security programmes were staples of city life long before 9/11 and 3/11. Some urban planners are designing fortress-style residential complexes in remote locations. But most people think that these projects go too far, and for now there are few signs that the threats of terrorism are emptying out cities.

In fact, most urban scholars argue that European and American cities are experiencing a renaissance. Next month, for example, the London School of Economics is hosting an international conference on "The Resurgent City". City centres, animated by commercial activity, new cultural attractions and pedestrian-friendly design, are bursting with life.

Consider London, where the recently renovated Trafalgar Square and South Bank walkway, the London Eye, British Museum courtyard and Tate Modern have revitalised the public sphere, boosting civic spirit and attracting unprecedented numbers of visitors. Immigrants, who could easily become scapegoats in a war on terrorism, are playing leading roles in this renewal, enlivening the city with entrepreneurial energy and cultural contributions that improve the urban environment for everyone.

We should put the recent attacks in context before giving up on the city or surrendering to the culture of fear. The bombing in Madrid killed 200 people and injured 1,400. Last summer, during a prolonged heatwave, more than 30,000 Europeans in excess of the norm died (15,000-plus in France, 6,000 in Spain and 2,000 in England) and thousands more were hospitalised. The US had a similar, though less deadly experience in 1995. But despite warnings from scientists, who predicted a recurrence, no one acted until it was too late.

Global warming (which even the Pentagon is now treating as a matter of urgent concern) combines with the increased aging and isolation of European and US populations to create a formula for new kinds of disaster. So, too, do health hazards such as HIV/Aids and influenza, which kill many more Europeans than do terrorists. But which governments are fighting a war on them?

The risks of further attacks on cities are real and serious, and every metropolis must step up its security programmes while preparing for an assault with biological or chemical weapons. Today we do have more to fear than fear itself. But as the Spanish protesters showed on 12 March, cities are where we can overcome this anxiety together.

Eric Klinenberg is assistant professor of sociology at New York University. His recent book Heatwave: a social autopsy of disaster in Chicago won the Urban Affairs Association award for best book in urban policy and was the British Sociological Association book of the year on health and illness in 2003