We are fortunate to live in a characterful, human-sized city

Norman Foster, the architect, recently opined that 'megacities will save mankind' - a megacity being one with more than 10 million inhabitants.

By 2050, he said, 70% of people will live in cities (over 50% already do).He measured cities' success mainly in terms of pollution control, economic growth, cycleways, mayors.

I think we are lucky, here in Brighton and Hove, not to live in one of Lord Foster's megacities. To live in a city that still retains its human scale. Of course it has its problems, some of which it shares with megacities.

Property prices have escalated out of all proportion, so that many ordinary people can barely afford to live here. (In a move that has been dubbed 'social cleansing', council staff have allegedly been instructed to advise residents struggling on benefits to move elsewhere).

We have too many people and too much traffic, pollution is excessive, and our demographic balance is awry - with too many students and incomers, too few older indigenes. Our city is stressed by its very popularity and success.

But it is still a city that feels individualistic and human, that you can walk about in with pleasure. I'd say it is already quite big enough. Once a city gets bigger than this, it becomes impersonal, mechanistic.

Cyril Connolly said 'no city should be too large for a man to walk out of in a morning'.

Historically, the world owes far more to small cities than to megalopolises.

The Athens of Plato and Aristotle, Alexandria in the time of Cleopatra, Baghdad in the time of Harun al-Rashid,Renaissance Florence, Shakespeare's London, Delhi in the time of the Mughals, Goethe's Weimar - all were compact communities where people knew who they were and what they belonged to.

By contrast, many of the world's fanciest modern megacities strike me as soulless, dehumanising ant-heaps. Out of them may come stupendous production statistics, but nothing and nobody that will be valued in 500 years' time.

Many of them, especially in China, are cities on steroids, with their hubristic regiments of skyscrapers, their 50-lane highways, and the human cost of their enforced bloatedness is horrific.

The air in Beijing is unbreathable, there are one million people living in underground missile shelters, while many of the traditional hutongs have been bulldozed by developers. Shanghai has swollen to 20 million.

Shenzhen, 60 years ago, was a fishing village: it will soon have 15 million, and eventually, according to terrifying plans, it and eight other nearby mushroom cities, including Guanzhou, will be merged to form the world's largest connurbation, at 42 million - outstripping even Tokyo, which has more people than Canada.

Too many of these huge cities' inhabitants live in appalling poverty. Half of Mumbai live in slums. Pope Francis, just last week, visited Nairobi's shanty towns. Altogether, one-sixth of the world's population, a billion, inhabit favelas, ranchos, bidonvilles, bustees.

We have to hope - as our poor are priced out, while trendy architects design luxury towers for overseas investors - that our own city does not become equally polarised.

Laurens van der Post said cities needed 'to grow smaller, not bigger; then, paradoxically, in terms of real meaning they will gain. Cities no longer fulfil the purpose for which they were invented.'

Where will it end? In Italo Calvino's novel Invisible Cities (1974), Marco Polo arrives in the city of Trude to find it is identical with the city he's just left. He is told he can leave it whenever he likes, but will only arrive at another Trude, 'absolutely the same, detail by detail.

The world is covered by a sole Trude, which does not begin and does not end. Only the name of the airport changes.'