Castelnau is a road in Barnes, in the London Borough of Richmond upon Thames, south west London, approximately 5.1 miles (8.2 km) west from Charing Cross on the south side of the River Thames. About 1.1 miles (1.8 km) long, it is the main road south from Hammersmith Bridge and forms part of the A306 road. It was originally named Upper Bridge Road. The name Castelnau is also used informally for Castelnau Estate and the area surrounding the road. An area of Barnes including Castelnau was designated a conservation area in 1977.