 The southern and western parts of the walls were originally faced with a local ashlar sandstone with a core of basalt rubble; the sandstone was mostly quarried at Howick.The sandstone has since been stripped from the western parts of the wall, and the sandstone along the eastern end of the walls gives way to small limestone blocks, originally only laid 11-foot (3.3 m) high with a 4-foot 11 inches (1.5 m) parapet, but later raised in height with additional basalt boulders, probably during the Wars of the Roses.It is uncertain if the curtain wall originally extended above the cliffs along the northern edge of the castle.