The City of London, widely referred to simply as the City, is a city, ceremonial county and local government district that contains the ancient centre and constitutes the primary central business district (CBD) of London and one of the leading financial cities of the world.
It constituted most of London from its settlement by the Romans in the 1st century AD to the Middle Ages, but the modern area named London has since grown far beyond the City of London boundary. The City is now only a small part of the metropolis of Greater London, though it remains a notable part of central London. Administratively, the City of London is not one of the London boroughs, a status reserved for the other 32 districts (including Greater London's only other city, the City of Westminster). It is also a separate ceremonial county, being an enclave surrounded by Greater London, and is the smallest ceremonial county in England.
The City of London is known as the Square Mile. Both the terms the City and the Square Mile are often used as metonyms for the UK's trading and financial services industries, which continue a notable history of being largely based in the City. The name London is now ordinarily used for a far wider area than just the City. London most often denotes the sprawling London metropolis, or the 32 Greater London boroughs, in addition to the City of London itself.
The local authority for the City, namely the City of London Corporation, is unique in the UK and has some unusual responsibilities for a local council, such as being the police authority. It is also unusual in having responsibilities and ownerships beyond its boundaries. The corporation is headed by the Lord Mayor of the City of London (an office separate from, and much older than, the Mayor of London).
The City is made up of 25 wards, with administration at the historic Guildhall. Other historic sites include St Paul's Cathedral, Royal Exchange, Mansion House, Old Bailey, and Smithfield Market. Although not within the City, the adjacent Tower of London, built to dominate the City, is part of its old defensive perimeter. The City has responsibility for five bridges in its capacity as trustee of the Bridge House Estates: Blackfriars Bridge, Millennium Bridge, Southwark Bridge, London Bridge and Tower Bridge.
The City is a major business and financial centre, with both the Bank of England and the London Stock Exchange based in the City. Throughout the 19th century, the City was the world's primary business centre, and it continues to be a major meeting point for businesses. London came second (after New York) in the Global Financial Centres Index, published in 2022. The insurance industry is located in the eastern side of the city, around Lloyd's building. The legal profession forms a major component of the northern and western sides of the City, especially in the Temple and Chancery Lane areas where the Inns of Court are located, of which two—Inner Temple and Middle Temple—fall within the City of London boundary.