London, England has no single definition. The name (which is pre-Roman in origin) usually encompasses at least the area occupied by the City of London (the "Square Mile"), the City of Westminster (the "West End") and parishes to the east of the City of London (the "East End"). Originally, London existed only north of the River Thames. The area accepted as "London" gradually increased to include what was termed "Metropolitan Middlesex", Lambeth and Southwark. This was formalised in 1889 with the formation of the County of London, which incorporated parts of Middlesex, Surrey and Kent. In 1963 this progressed further with the creation of Greater London, including the rest of Middlesex and parts of Essex and Hertfordshire.