Between Richmond and the North Sea, thirty bridges cross the Thames. They carry people across a stretch of river 35 miles long, bringing together a population of nearly eight million. These extraordinary structures have been the making of London, Britain's capital, and according to Dan Cruickshank, Europe's greatest city. Dan's exploration of the mysteries of London's Bridges starts in the far east of London in the marshes of the Thames estuary, the story then moves upstream to Vauxhall, where archaeologists are recording London's oldest crossing, built for religious reasons in the Bronze Age, three and a half thousand years ago. Thereafter it was 1500 years before the Romans built the first proper bridge, spanning the Thames near the site of today's London Bridge. That too was swept away, and it was only in the twelfth century that the famous London Bridge which entered legend, was built. Old London Bridge presided over a very different London from today's a riverside world of water pageants and frost fairs when the whole river froze over. But from the eighteenth-century, London's growth required many more bridges, starting with Westminster Bridge in the political heart of England, which transformed London into a mega-city of millions of people on both banks of the Thames. The film continues with the engineering triumphs of the Victorian period at Hammersmith and Tower Bridge, and eventually the heroic Dartford Bridge which spans the river near the very marshes where Dan began his story. We conclude with the jewel-like Millennium Bridge, and Dan's hope that maybe one day, a true replacement for Old London Bridge will be built.