When the construction of a modern port was planned in Sète, Pierre-Paul Riquet did not want it to cross the Aude river to reach the city. The architect of the Canal du Midi wanted to avoid many navigation difficulties. He therefore chose to drill a tunnel under the Ensérune hill and a staircase of locks near the arrival in Béziers. The result of this venture is the Malpas tunnel, drilled over a length of 557 feet (170 m) in the sandy sandstones of Ensérune's heights.