Bateau passant l'écluse de Castelnaudary

This 4-chamber staircase lock allows boats to cross the significant height difference between the Castelnaudary basin and the canal 10 m lower down. The booming flour milling industry of the past has also made its mark on the area.

4 Saint-Roch lock chambers to cross the significant height difference

Ecluse St-Roch, Castelnaudary - V. Hadengue

Ecluse St-Roch, Castelnaudary - V. Hadengue

Did you know?

The lock bears the same name as a chapel devoted to Saint Roch that is still standing on the left bank, upstream from the lock. Saint Roch was born in Montpellier in around 1350 and was known for protecting the communities from the plague. Chapels devoted to Saint Roch are often built outside the enclosure of medieval towns, in areas of quarantine. A mass was held at this church on 17 May 1681 to celebrate the departure of the first barges navigating between Castelnaudary and Sète. This building is on private property and is not open to the public.

This 4 chamber staircase lock was built in 1678 as a necessity to cross the 9.42 m to reach the canal after leaving the Grand Bassin of Castelnaudary.

The water supply needed to operate this quadruple lock is provided by the water stored in the Grand Bassin upstream. The Saint-Roch lock has been listed as a Historic Monument since 1996.

Did you know?

The first locks built by Riquet only had one lock chamber (single lock). When there was a significant height difference to cross, the manoeuvres were complicated and the structures became weaker. Therefore, to cross significant differences in height, Riquet designed locks with 2 to 8 chambers!

Fonseranes lock in Béziers is the most impressive, with 8 chambers, crossing more than 20 m difference in height! Saint-Roch lock is the only quadruple lock on the canal and comes just behind Fonseranes in terms of size.

Ecluse St-Roch, Castelnaudary

Ecluse St-Roch, Castelnaudary

Mills operated by the power of the water

The decree of construction for the Canal Royal du Languedoc (former name of the Canal du Midi), signed in 1666, authorised the owner of the fiefdom, Pierre-Paul Riquet, to build mills that would be operated by the power of the excess waters available on the canal. Taking into consideration the fact that the economy of the port was based on the cereal trade and that there was a great difference in height at this lock, Riquet decided to build a mill here. This first construction was put into operation in around 1681. It was built on the right banks of the lock, right next to the upstream pound.

A second mill was built in around 1750. This lower mill was separated from the upper mill by a broad embankment. The millstones of both mills were operated by water wheels, which were horizontal wheels with blades, turned by water that arrived along a chute.

In 1832-1833, a flour mill was built between the upper and lower mills, to grind the wheat and make the flour which would then be mainly exported. It was comprised of a ground floor and two upper floors, and was equipped with a horizontal wheel that was believed to be more powerful than the water wheel mechanism. The other machines inside the flour mill were operated by a wheel mechanism in the lower mill. The water used to power the mills would then flow along an outlet channel and back into the canal, downstream from the lock. This water was therefore also used for navigation.

In 1873, the Compagnie des Chemins de Fer du Midi, in charge of managing the canal, introduced a modernisation plan to establish a flour production hub in Castelnaudary. Two industrialists applied to take on the tenancy of the mills. The flour mill was extended upstream and another level was added. New machines were also installed, including a new turbine with cast iron tank. The millstones at the upper mill were no longer used and this became housing for the farmer.

In 1892, farmers were given authorisation to install a steam-operated mechanism to operate the millstones and flour mill machines.