This is all that remains of a former abbey founded in the 5C by St Cassien. The church was rebuilt around 1040 and sturdy fortifications added. Don't miss the 5C crypt nor the St Victor cave and the catacombs where St Lazarus and St Mary Magdalene are venerated. You can also admire antique, pagan and Christian sarcophagi, including that of St Cassien, discovered in 1965, containing the remains of two martyrs. The abbey was built above their tomb.