This guide takes the walker from the Thames Barrier in London to the source of the Thames 180 miles away in rural Gloucestershire. The towpath route, opened as a national trail in 1996, has been improved by the addition of new footbridges and the creation of 20 miles of new riverside path. More than 90 per cent of the Thames Path is either public footpath or bridleway. The Thames, once an important water highway, links a string of historic sites. In the capital there is Greenwich, the Houses of Parliament and Lambeth Palace. Hampton Court Palace lies just outside London, and before reaching Windsor there is riverside Runneymede where King John agreed to the Magna Carta. The water and towpath in the Upper Reaches can be both beautiful and lonely, with cormorants, herons and swans, as appreciated by Shelley and William Morris. The climax is the 22 miles of the infant Thames leading to a field with its often dry spring situated just below the Roman Foss Way.