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Heritage classified

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Origin and history

The water intake of Alzau, located in the town of Arfons in the Tarn, marks the starting point of the mountain channel, a hydraulic work essential to power the Canal du Midi. Built in the second half of the 17th century according to the plans of Pierre-Paul Riquet, it captures the waters of the Alzau River, the most important stream of water in the system. The water is then moved to the plain channel and then to the canal via a partially underground 150-metre network. A low road made of irregular stones, surmounted by a metal strip, makes it possible to divert the water to the holding structure, equipped with valves (including some modern) and behind the scenes of sledges inherited from the original system.

To validate his project with Colbert, Riquet had a test pipe built (the Coudières roadway) to prove the feasibility of capture. Alzau, 680 metres above sea level in the Black Mountain, also includes a guard house and a memorial erected in 1837 by the Duke of Caraman, descendant of Riquet. This site, classified as a historical monument in 1998, has also been a UNESCO World Heritage Site since 1996, as part of the Canal du Midi, a masterpiece of hydraulic engineering in the Grand Century.

The early 17th century work underwent modifications in the 19th century, notably on the valves and the downstream glacis in rubble, repaired several times. The gutter of the Mountain, conceived as an essential arrangement to power the canal, illustrates the technical audacity of Riquet, who realized the "Deux Mers Canal" between 1667 and 1682. Today, the site preserves traces of its original features, such as a semi-mural vault behind the valves or foundations of the guard house, testimony to its historic role in the canal's water supply.

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