Without the Thames there would be no London. From earliest times, the city"s needs --whether for stone, gold or coal, for hay to feed livestock or food, or wine and spices for human beings -- were supplied from the river, as the fierce tides brought ships upstream or carried them down again. Only with the age of trunk road and rail did London"s global importance as a port diminish. Even after that the tides continued to drive the great power stations. Gavin Weightman"s fascinating book is the best possible introduction to the water and its ways, the buildings that line the banks, and the people who lived by the river, their customs and ancient knowledge. The Thames is here in every guise -- highway and barrier, source of power and source of life, place of entertainment, port, and drainpipe. Above all one feels the presence of the great waterway itself, a force of nature in our urban midst.