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).
( It ( ( has ( served ( as ( ( ( a fortress ) ( for ( ( ( ( ( ( ( ( the Gallo-Romans ) , ) ( the Visigoths ) ) , ) Franks ) , ) and ) ( medieval French ) ) ) ) ( -LRB- ( ( you ( can ( ( see ( ( the layers ) ( of ( their masonry ) ) ) ) ( in ( the ramparts ) ) ) ) ) -RRB- ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ has) (VP (VBN served) (PP (IN as) (NP (NP (DT a) (NNS fortress)) (PP (IN for) (NP (NP (DT the) (NNP Gallo-Romans)) (, ,) (NP (DT the) (NNPS Visigoths)) (, ,) (NP (NNP Franks)) (, ,) (CC and) (NP (JJ medieval) (NNS French)))) (PRN (-LRB- -LRB-) (S (NP (PRP you)) (VP (MD can) (VP (VB see) (NP (NP (DT the) (NNS layers)) (PP (IN of) (NP (PRP$ their) (NN masonry)))) (PP (IN in) (NP (DT the) (NNS ramparts)))))) (-RRB- -RRB-)))))) (. .)))
Various people have used it as a fortress, as can be seen from the layers of masonry.
( ( Various people ) ( ( have ( ( ( ( used it ) ( as ( a fortress ) ) ) , ) ( as ( can ( be ( seen ( from ( ( the layers ) ( of masonry ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Various) (NNS people)) (VP (VBP have) (VP (VBN used) (NP (PRP it)) (PP (IN as) (NP (DT a) (NNS fortress))) (, ,) (SBAR (IN as) (S (VP (MD can) (VP (VB be) (VP (VBN seen) (PP (IN from) (NP (NP (DT the) (NNS layers)) (PP (IN of) (NP (NN masonry)))))))))))) (. .)))