Welcoming the inevitable.

'Stadtluft macht frei', as the German medieval adage had it: 'Town air makes free'. For all the difficulties associated with urbanisation, particularly since the industrial revolution, that adage holds good. It was difficult for medieval monarchs, just as it is difficult for modern dictators, to suppress the culture of cities. Their wealth-producing nature, and their inherent concentration of citizens give them economic and political influence which has proved even greater than that previous measure of power--land ownership. Yet the study of cities, and the relationship between the various conditions and forces which influence their development, has rarely been at the top of the architectural agenda. This may have been the result of embarrassment at the legacy of the Corbusian Modernists, who viewed helplessly the dilution of profound and powerful ideas by weak or cynical clients, and technological developments unseen by the pioneer Modernists, for example the environmental impact of the car. It may also be that the attractions of designing object buildings outweigh the complicated and long-term business of creating new areas for urban life.

The fact that the 2006 Venice Biennale is devoted to the subject of cities is therefore thoroughly welcome, and this issue of The Architectural Review gives a flavour of its subject matter. What is encouraging about the spirit of the Biennale, curated by Richard Burdett, is the refusal to treat city growth simply as a problem or threat, but rather as offering rational choices as to how those cities determine their futures. In other words, city planning is regarded as the opportunity to create desirable conditions, not the occasion for passing the smelling salts.

'Mega-cities' will become, if not a commonplace, then certainly more common across the globe and across this century. Those responsible for them (and that means mayors, planners, engineers and architects taking decisions today), have at least one advantage over their forebears: enough knowledge to avoid the worst of the mistakes made by the first wave of industrialising cities, and to note the crucial importance of decisions over infrastructure, waste management and what is sometimes called the 'ecological footprint' of a city in determining its future shape and size. They will also have to take account of a new element in the urban condition: the atomising effect of digital technology on the lives of individual citizens and cultural sub-groups. The complexity of this emerging condition will equal the complexity of cities themselves.