Berkeley Square is a town square in Mayfair in the West End of London, in the city of Westminster. In 1696, Berkeley House on Piccadilly was sold to William Cavendish, 1st Duke of Devonshire, who was obligated by the land deal to not build on the land that he retained behind the house. In 1798, very large London Plane trees were planted at the Square, which was opened to the public. It was originally a mostly residential area, but it was later taken over by offices, including a number of hedge funds and wealth management businesses.