Template:Infobox UK place Castelnau is a road in Barnes, in the London Borough of Richmond upon Thames, south west London, approximately Template:Convert west from Charing Cross on the south side of the River Thames. About Template:Convert long, it is the main road south from Hammersmith Bridge and forms part of the A306 road. It was originally named Upper Bridge Road.<ref name="Castelnau">The History of Castelnau, Holy Trinity Barnes, 1968</ref>
An area of Barnes including Castelnau was designated a conservation area in 1977.
The name Castelnau is also used informally for Castelnau Estate (see below).
Castelnau means "new castle" in the Occitan language.Template:Citation needed
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.Template:Citation needed
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, Template:Citation neededand 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.<ref name="Cherry and Pevsner"/>
Major Charles Lestock Boileau built Castelnau Villas (now 84–122 and 91–125 Castelnau), designed by the architect William Laxton,<ref name="Cherry and Pevsner">Template:Cite book</ref> 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.<ref name="Castelnau"/>
In 1926, London County Council built a cottage-style estate of 640 houses, called Castelnau Estate, on the site of a market garden.<ref name="BM Past">Maisie Brown: Barnes and Mortlake Past with East Sheen, Historical Publications Ltd, ISBN 0948667 46X</ref> 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.<ref name="Castelnau"/>
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:
- Holy Trinity Barnes
- Catholic Church of St Osmund, Barnes