Agde Cathedral (Cathédrale Saint-Étienne d'Agde), a Roman Catholic cathedral located in Agde in the Hérault département of southern France, was constructed in the 12th century on the foundations of a 5th century Roman church, formerly a temple of Diana.
It was formerly the seat of the Bishop of Agde. The see was not restored after the French Revolution and by the Concordat of 1801 its parishes were added to the Diocese of Montpellier.
The cathedral is remarkable for its use of black basalt from the nearby volcanic Mont St. Loup quarries.
The building is extremely strong and was able to serve as a fortress as much as a church: the walls are between 2 and 3 metres thick, and the square tower, 35 metres high, could also function as a keep.
In the severe interior the 17th century high altar of polychromatic marble stands out all the more, as do the organs in Baroque style.