The City of London is a city, ceremonial county and local government district that contains the historic centre and the primary central business district of London. It constituted most of London from its settlement by the Romans in the 1st century AD to the Middle Ages, but the modern city named London has since grown far beyond the City of London boundary. The City is now only a tiny part of the metropolis of London, though it remains a notable part of central London. Administratively, it forms one of the 33 local authority districts of London; however, the City of London is not a London borough, a status reserved for the other 32 districts. It is also a separate ceremonial county, being an enclave surrounded by Greater London, and is the smallest ceremonial county in the United Kingdom.
The City of London is widely referred to simply as the City and is also colloquially known as the Square Mile, as it is 1.12 sq mi in area. Both of these terms are also often used as metonyms for the United Kingdom's trading and financial services industries, which continue a notable history of being largely based in the City.