Profile At its western end, Toulouse, the canal is at an altitude of and climbs to at its summit level between Ocean Lock and Mediterranee Lock west of Castelnaudary before dropping down to sea level at Sète. The graph shows the profile of the Canal du Midi from Toulouse (1), through the summit of the canal at Seuil de Naurouze (2), Castelnaudary (3), then Carcassonne (4) and Trèbes (5). The channel continues to Béziers just after Fonsérannes Lock (6), and then on to Agde (7) before flowing in to the Bassin de Thau at Sète (8). At , Naurouze is the highest point of the canal with a drop of between the summit and Toulouse and between the summit and Sète. The longest pound is between Argens Lock (Aude) and the Fonsérannes Lock (Hérault) while the shortest reach is between two locks at Fresquel. Locks The following list numbers the locks from the Canal lateral a la Garonne in the west to the Bassin du Thau in the east. Staircase locks are listed as a single entity but the number of individual chambers in the flight is noted. Travelling west to east from Toulouse to Sète the locks numbered 1–18 are ascending and 19–86 are descending. Castanet lock is the first lock with an elliptical chamber, as Riquet realised it was the best fit solution due to mechanical stress from surrounding areas. See also Aqueducts on the Canal du Midi Water features on the Canal du Midi Notes Lock numbers are as given in the appendix of the 1994 edition From Sea to Sea by L.T.C. Rolt The flight at Fonserannes was "replaced" by a water slope in 1984 hence the single "lock number". However, the slope has never worked and the 6 flight staircase remains the only way to pass through meaning that there are 91 locks but only 86 numbers. Chamber has three sets of gates, the third being the junction with the branch descente dans l'Hérault References