Any thriving city is a wonder of human nature, with people flocking together as citizens, attracted by its set-ups for collective thinking and playing, communication towers, modified water ways, emporiums of far-fetched items and new ideas, the excitements of diversity and chance. Sealed beneath it all is an intricate system of pipes and lines like the roots of a giant tree. It is built up from our immemorial tinkering with raw materials, earth, water, air, fire. No other creature produces such Ozymandian insect-mounds. Even in the dead of night there's a low continuous sound, like the seething murmur inside a hive of bees.