Towers, usually round, were placed at the corners and along the walls in the Phillipienne castle, close enough together to support each other. The walls had two levels of walkways on the inside, a crennellated parapet with merlons, and projecting machicolations from which missiles could be dropped on besiegers. The upper walls also had protected protruding balconies, "échauguettes" and "bretèches", from which soldiers could see what was happening at the corners or on the ground below. In addition, the towers and walls were pierced with arrowslits, which sometimes took the form of crosses to enable a wider field of fire for archers and crossbowmen.