Is '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).' a logical precursor to the hypothesis 'The fortress has been knocked down several times.'
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 has been knocked down several times.