As we worry about the best ways of preserving our heritage, US concerns centre on keeping Philadelphia standing. In one six-day period in August, 25 buildings collapsed.
This was the culmination, exacerbated by a wet summer, of a process which has been going on for years. Until now, the typical collapse rate was 20 buildings in a whole year. The main cause is depopulation of the city centre, coupled with the boggy ground onto which the city expanded from its original core.
Police helicopters have been patrolling the most dilapidated areas, looking for missing roofs, while hard hats are this autumn's fashion accessory.