In the context of 'It has served as a fortress for the Gallo-Romans, the Visigoths, Franks, and medieval French (you can see the layers of their masonry in the ramparts).', does 'The fortress was built by the medieval French in 1173.' stand alone without direct association?
It has served as a fortress for the Gallo-Romans, the Visigoths, Franks, and medieval French (you can see the layers of their masonry in the ramparts).###The fortress was built by the medieval French in 1173.