Piccailly is a major London street, running from Hyde Park Corner in the west to Piccadilly Circus in the east. It is completely within the City of Westminster. The street is part of the A4 road, London's second most important western artery. St. James's lies to the south of the eastern section of the street, while the western section is built up only on the northern side and overlooks Green Park. The area to the north is Mayfair.