The Aqueduc de Castries (Castries Aqueduct) is the largest hydraulic structure ever created in France for a private individual. It was the brainchild of René-Gaspard de la Croix de Castries, who requested help from Pierre-Paul Riquet, the bold engineer who designed the Canal du Midi, when he was tasked with bringing water to the Château de Castries park by the illustrious landscape architect André Le Nôtre.
Made from local Castries stone, the aqueduct is 6,822 metres long and only slopes by 3 metres. Its most spectacular section, the great arches which stand about twenty metres high, is close to the town's historical centre.
The Castries tourist information office organises guided tours on foot or by horse-drawn carriage on request. Another way to explore it is from a hiking trail.