The castellologist Philippe Durand gave a detailed description of the Philippian castral model applied to the Guédelon construction site. Its functional and rational architecture illustrates a change in design: the building is no longer withdrawn into itself but is part of a system that allows it to be rescued. This military castle has a geometric plan with buildings laid out regularly on the backs of the curtain walls and is protected by a masonry ditch. Its dimensions are modest (229 ft / 70 m sides at most) to allow better defense. The blind curtain walls, about 33 ft (10 m) high, are crowned with a walkway. The circular towers, 26 to 33 ft (8 to 10 m) in diameter and 49 to 65 ft (15 to 20 m) high, rise on three internal levels. They are placed at the corners and in the middle of the sides and defended by simple loopholes. Access is between two towers through a door equipped with numerous stopping elements (killer, portcullis, side loopholes). The detached keep is placed at an angle of the complex.