Chateau Gaillard had utilized the last of the newly built, huge great towers, and Rochester had depended on its early twelfth-century tower. During the course of the thirteenth century defense shifted to a towered wall, the enceinte or enclosure castle. Two plans emerged: the castle could rely on a series of courtyards, which had to be taken one after another, or on a concentric defense in which a second wall entirely surrounded the inner wall.

Ch. 2 : The Castle as Fortress : The Castle and Siege Warfare - Medieval castles (2005)