This is where the Canal du Midi was inaugurated on 19 May 1681, officially opening the waterway to navigation.
Initially, the route of the Canal du Midi did not pass through Castelnaudary. The city, together with the diocese of Toulouse, financed the change of route to a total 30,000 pounds, which allowed Castelnaudary to become the most important port on the whole canal.
Around the basin there were stores for drying wood, rope makers, boatmen, boat repairs, carpenters and drinking troughs. Various trades linked to the boat industry settled there, leading to a major economic boom for the town.
Located between the four St Roch locks and the old bridge, the Grand Bassin is exposed to wind from all sides. Manoeuvring being difficult there, a breakwater was built: the île de la Cybèle. There was an open-air café there until the 1940s.
Today, taking a walk around the rest of the Grand Bassin is a pleasure. Between the trees and the water, this is where visitors have the best view of the town.