London is the capital and largest city of England and the United Kingdom, with a population of just over 9 million.^[9] It stands on the River Thames in south-east England at the head of a 50-mile (80 km) estuary down to the North Sea, and has been a major settlement for two millennia.^[10] The City of London, its ancient core and financial centre, was founded by the Romans as Londinium and retains boundaries close to its medieval ones.^{[note 1][11]} The City of Westminster, to the west of the City of London, has for centuries hosted the national government and parliament. Since the 19th century,^[12] the name "London" has also referred to the metropolis around this core, historically split between the counties of Middlesex, Essex, Surrey, Kent, and Hertfordshire,^[13] which largely comprises Greater London,^[14] governed by the Greater London Authority.^{[note 2][15]}