There's a scary book called 'Blood River' about the collapse of civilisation in Congo; its most frightening moment is when the author tells of discovering the relics of a railway in the middle of a forest, as if it was ancient archaeology. Yet Julien Temple's documentary about Detroit shows us that the west should not necessarily be so smug. The rate at which nature is reclaiming the motor city from man is alarming; if you want to know how long humanity might survive some disaster that took the impetus out from the economy, the answer is apparently just a few decades. The cause in Detroit's case is as follows: the collapse of the U.S. car industry; the availability of land and of cars (increasingly built elsewhere) to facilitate commuting from outside the city limits; and a tax system that provides no breaks to depopulating communities. The film combines a concise history of the city with footage of its increasing dereliction and a soundtrack taken mainly from its rich musical history; except for some odd, intrusive sound effects, it's mostly excellent and gripping. But above all else, proof that one doesn't need to travel to Africa to witness the descent on man.