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-)))))) (. .)))
The fortress was built by the medieval French in 1173.
( ( The fortress ) ( ( was ( built ( by ( ( the ( medieval French ) ) ( in 1173 ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NNS fortress)) (VP (VBD was) (VP (VBN built) (PP (IN by) (NP (NP (DT the) (JJ medieval) (JJ French)) (PP (IN in) (NP (CD 1173))))))) (. .)))