The River Thames is best known for being the capital's river,
but only a small percentage of it runs through London. It begins
its 215-mile1 journey at Trewsbury Mead in Gloucestershire,
winds its way through and between a further eight English
counties, and passes through towns and cities such as Oxford
(where it is known as the River Isis), Reading, Henley,
Maidenhead, Windsor, Kingston and Teddington before it becomes
tidal at Teddington Lock, arrives at London, sweeps past Tilbury
and Canvey Island until it meets the sea between Southend in
Essex and Sheerness in Kent. The river is joined by many
tributaries (some now underground) and canals all the way from
beginning to end. Without the River Thames, there would have
been no London. In 43 AD the Romans sailed up the river and
chose the first place that was suitable to bridge. A pair of
gravel hills divided by a small stream and surrounded by streams
and bogs must have appeared to be easily defensible on the north
bank, with firm footing on the other side