Ancient Roman ruins. Source iStock.

+ People are the city’s primary infrastructure: they make and remake cities over time, or abandon them to decay.

I’m writing this from Belgrade – a city that, 13 years ago, was the target of a NATO bombing campaign designed to subject it to stresses that would paralyse its infrastructure and dissolve its government.

The regime collapsed, Belgrade survived.

Many overstressed cities have historically vanished. The physical resources available to a city are critical to its success or failure, but people are the city’s primary infrastructure. It’s they who will make and remake cities over time, or abandon them to decay.

I’ve been to megacities like Tokyo, Mexico City and São Paulo, and I’ve spent quite a lot of time in India, but the three cities I know best are Austin, Belgrade and Turin. Observing life in these three cities shaped my thoughts on this topic.

As a futurist, one should learn from the past. History shows us that the mere size of cities doesn't predict their collapse. A megacity can have sufficient resources, resiliency and political will, just as a small village can exhaust its resource base and vanish.

In the past, Rome was a megalopolis that fell apart completely – its population crashing from over a million and a half to maybe a few dozen thousand. There were people herding cows in the ruins of the Coliseum.

More recently, I’ve seen small towns around Turin, and around Belgrade that are in headlong collapse. People have sought opportunities elsewhere. Schools are empty. Agricultural markets have gone. In the Balkans, this has often been the result of new political borders that have severed trade links and cut off the flow of human energy.

Ancient cities have survived against the odds. Belgrade has been burnt down 19 times in its history. But its location in fertile land, at the strategic confluence of the Danube and the Sava, means it has bounced back. Today Belgrade once again feels like a city that’s making positive progress.

So how can we ensure successful, long-lived cities? Of course, there’s never been a perfect city (and there never will be). Stresses are usually about specific resources like air, fuel, water or topsoil. But if you look at cities that have failed and been abandoned, you’ll usually see a fairly simple cause. Maybe the water supply has run out, or the topsoil has salted, for example.

I’m not an urban designer, but for me the question we need to ask is: what do you want from your city? Do you want it to thrive on trade? Do you want it to be rich in culture? Do you value quality of life? Do you want it to be a fortress against your enemies, as Turin once was?

It's useless to design a city without understanding the demands of that city’s inhabitants. What will get them out of bed in the morning? How will they be motivated to engage in urban life? The answers to these questions will change over time.

I think some of the most rewarding cities to live in are those that have formed a ‘layer cake’ of remaking and reusing. Walk around the old districts of Turin and you see how people have retrofitted historic buildings – there are fibre optic cables emerging from the same walls where disused gas lamps hang.

For me, this conveys the feeling of a human civilisation fully lived, as people forget the original purpose of buildings and re-inhabit them. We have more and more built infrastructure, and a deeper and deeper architectural heritage. So we have to keep inventing ways to repurpose these structures.

Achieving this is more down to political design than physical design. There are political interventions that would make cities much more ductile. For example, reforming zoning and planning restrictions could enable people to repurpose buildings much more quickly.

It will take economic vitality and ambition. Although it will require new methods of production (like the steel frames that prompted the skyscraper boom), it has to be about more than architecture. It needs political reform.

We need a piece of techno-political-social-cultural magic that unleashes creativity in such a compelling way that people recognise it as the way forward. It has to be more than a theoretical argument; it has to be a lived experience. In any historical period some cities represent modernity; lesser cities follow.