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. Plans became more compact, and buildings filled the space around the wall of the inner bailey. Towers were added to the walls, developing a true curtain wall (so called because it “hung” between towers) in which every section could be seen and defended from projecting towers. The towers themselves were rounded into cylindrical or D-shapes so that no flat surface tempted a battering ram, and every surface could be surveyed. Wherever possible, stone replaced wood at the top of the wall. Stone machicolations replaced wooden hoardings.