Gisors is a small town near the beginning of Normandy that was famous as a fortress of the English to preserve their hold on a large chunk of Western France.  King William ordered a formidable medieval castle in 1095 to be built on the highest point in the town to protect its eastern border from French encroachment.  Learn more of this fortress here:  <https://en.wikipedia.org/wiki/Chateau_de_Gisors>