The Thames flows entirely within England, United Kingdom, stretching 346 km (215 mi) from its source in the Cotswolds (Gloucestershire) to the North Sea at the Thames Estuary.
Roman Londinium founded at its lowest bridging point. Medieval trade, Tudor pageants, Victorian sewage crises (the "Great Stink"), and modern revitalization (Thames Path, Thames Barrier) all center on this river. Today it supplies drinking water, supports rowing/sailing, and defines London's identity.