The Brescou Fort lies a few kilometres off the Cap d'Agde and was built on the submerged part (5,000 m2) of an ancient underwater volcano. It could have been the entrance to the magnificent harbour that Cardinal de Richelieu dreamed about, but work was stopped after he died.
The Brescou Fort was built by the Vicomte de Joyeuse in 1586, during the wars of religion, the fort initially had a defensive role. Sadly, its modest fortifications were unable to resist Montmorency's revolt and it was entirely destroyed in 1632. Raised from its ashes, Brescou was built as we see it today in 1680, probably along the lines of plans drawn up by Vauban.
Brescou's true role was that of State prison in the 18th Century, a sort of Bastille on the water. The Revolution imprisoned its suspects there, and the prison was finally closed in 1851.