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 (see below).
Three different English pronunciations of the word "Castelnau" seem to be in current use, all differing only in the final vowel: "castle know" is more ancient, and resembles the original French vowel, "castle now" is perhaps used to match with Nassau Road in the area, and "castle gnaw" is favoured by more recent inhabitants.
Castelnau takes it name from Castelnau-le-Lez, near Montpellier in France: in 1691, the 10th Baron of Castelnau and St Croix, a Huguenot, fled France for England following persecution,and his son, Charles Boileau, settled in north Barnes and his descendants developed parts of the area.
Castelnau was developed after the opening of Hammersmith Bridge in 1827.
Major Charles Lestock Boileau built Castelnau Villas (now 84–122 and 91–125 Castelnau), designed by the architect William Laxton, in 1842, followed by rows of cottages called Castelnau Row, Castelnau Place and Gothic Cottages. After his death in 1889, Upper Bridge Road was renamed Castelnau.
In 1926, London County Council built a cottage-style estate of 640 houses, called Castelnau Estate, on the site of a market garden. In 1971 these passed to ownership of Richmond upon Thames Council. Many are now privately owned. Many of the roads in this estate are named after Deans of St. Paul's who had been Lords of the manor of Barnes between the 14th and 17th centuries: Everdon, Kilmington, Alderbury, Kentwode, Howsman and Stillingfleet.
Castelnau is noted for 20 pairs of exceptional classical villas which were built in 1842 by Major Boileau (see above). There are also two churches:
- The History of Castelnau, Holy Trinity Barnes, 1968
- Castelnau Conservation Area
- Bridget Cherry and Nikolaus Pevsner (1983). The Buildings of England – London 2: South. London: Penguin Books. p. 470. ISBN 0 14 0710 47 7.
- Maisie Brown: Barnes and Mortlake Past with East Sheen, Historical Publications Ltd, ISBN 0948667 46X