The central keep—known as the White Tower—was begun about 1078 close inside the old Roman city wall and was built of limestone from Caen in Normandy. During the 12th and 13th centuries the fortifications were extended beyond the city wall, the White Tower becoming the nucleus of a series of concentric defenses enclosing an inner and an ... More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.