The fortress was designed to protect the saints' relics in the event of a Saracen raid: the upper chapel forms a keep surrounded at its base by a wall-walk and topped by a crenelated platform. The roof of the church is reached on a stairway with 53 steps. From here, there is a view over the sea, the rooftops of the town and the lakes. Inside (3rd row on the left) is the Saints' small boat, carried in a procession during pilgrimages. The reliquaries of the two saints (Mary Jacobe and Mary Salome) are in the upper chapel decorated with Louis XV panelling.