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.