River Fleet

The River Fleet is the largest of London's subterranean rivers. Its headwaters are two streams on Hampstead Heath, each of which was dammed into a series of ponds, the Hampstead Ponds and the Highgate Ponds, in the 18th century. At the southern edge of Hampstead Heath these descend underground as sewers and join in Camden Town. The waters flow 4 mi (6 km) from the ponds to the River Thames.

The river gives its name to Fleet Street, the eastern end of which is at what was historically the crossing over the river known as Fleet Bridge, and is now the site of Ludgate Circus.

The Fleet arises on Hampstead Heath as two sources, which still flow on the surface as the Hampstead Ponds and the Highgate Ponds. Then they go underground, pass under Kentish Town, join in Camden Town and flow onwards to King's Cross. King's Cross was originally named Battle Bridge, referring to an ancient bridge over the Fleet where Boudica's army is said to have fought an important battle against the Romans. The river then flows down Farringdon Road and Farringdon Street, and joins the Thames beneath Blackfriars Bridge.

The river's name is derived from the Anglo-Saxon flēot "tidal inlet". In Anglo-Saxon times, the Fleet served as a dock for shipping.

The higher reaches of the river were known as the Holbourne (or Oldbourne), whence Holborn derived its name.

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