of building. The division into three wards bears similarities with the design of Château de Chinon, built by Henry II in the mid-12th century on a promontory overlooking a town. The outer bailey is the southernmost feature of the castle; it is pentagon shaped and there are five towers spaced along the wall, three of which are at corners. North of the outer bailey is the middle bailey which is an irregular polygon; like the outer bailey, the wall of the middle bailey is studded with towers. The towers allowed the garrison to provide enfilading fire. In the fashion of the time, most of the towers in the curtain walls of the middle and outer baileys were cylindrical. Château Gaillard was one of the first castles in Europe to use machicolations—stone projections on top of a wall with openings that allowed objects to be dropped on an enemy at the base of the wall. Machicolations were introduced to Western architecture as a result of the Crusades. Until the 13th century, the tops of towers in European castles had usually been surrounded by wooden galleries, which served the same purpose as machicolations. An Eastern innovation, they may have originated in the first half of the 8th century. Within the middle bailey was the inner bailey. The gatehouse from the middle of the inner bailey was one of the earliest examples of towers flanking the entrance to remove the blind spot immediately in front of the gate. This was part of a wider trend from around the late 12th or 13th century onwards for castle gateways to be strongly defended. The design of the inner bailey, with its wall studded with semicircular projections, is unparalleled. This innovation had two advantages: firstly, the rounded wall absorbed the damage from siege engines much better as it did not provide a perfect angle to aim at; secondly, the arrowslits in the curved wall allowed arrows to be fired at all angles. The inner bailey, which contained the main residential buildings, used the principles of concentric defence. This and the unusual design of the inner bailey's curtain wall meant that castle was advanced for its age, since it was built before concentric fortification was fully developed in Crusader castles such as Krak des Chevaliers. Concentric castles were widely copied across Europe; for instance, when Edward I of England—who had himself been on Crusade—built castles in Wales