The round lock of Agde on the Canal du Midi connects the canal and the town of Agde in the Hérault department. This lock differs from classic locks as it has three gates while the others only have two. The round shape of the side walls allows the boats to maneuver inside the lock in order to choose their exit between the different gates. The round lock of Agde was built in 1676 and made of black basalt stone. The exits lead to Béziers (via the Portiragnes lock) for one, the Thau pond for the second, and Agde for the third.