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, alongside Canary Wharf, the primary central business district (CBD) of London and one of the leading financial centres 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.