CREATING AN ENTIRE city is something hard to plan, even now we know we are supposed to. Since Brasilia was founded in the 1950s, the brand-new customised city has, like the ex-urban garden suburb, gone out of fashion. Many of the cities with which we are familiar were laid out according to a great visionary experiment based on plans created over two millennia ago. The most enduring models are military: a grid of squares first promoted by Alexander the Great, or the castle or fort town on an important river or sea port. The model did not guarantee sustainability. What powered a city’s survival was its capacity to adapt to circumstances, not plans.

Whatever its first function – city state, sea port, market-town, imperial capital – an urban centre always needs a hinterland to support it. Cities on every continent have disappeared into desert or jungle because the lands that surrounded them were lost, stolen or worn out. Rome and Athens continue to adapt, but why did the civilisation of Medieval Zimbabwe disappear? The human tendency to destroy hinterland cannot be exaggerated. Before the first cities, human activity set the process of terminal environmental degradation in motion. Cute though they seem when marshalled by a ragged lad tootling a flute, insatiable goat herds have been a persistent and efficient agent of desertification ever since the dawn of pastoralism. The Romans de-forested Sicily to build their navies. The Greeks did the same to islands in the Aegean. These days, global cities require global hinterlands. And so their sustainability is an international issue.