How thick were castle walls?

Castle walls typically ranged in thickness from 3 feet (0.9 meters) to 15 feet (4.5 meters), although some walls could be as thick as 20 feet (6 meters) or more. The thickness of a castle wall depended on several factors, including the size and importance of the castle, the availability of building materials, and the level of military engineering knowledge at the time. Thicker walls provided greater protection against siege weapons and undermining, but also required more resources to build. Castle walls were often made thicker at their base, where they were more vulnerable to attack, and thinner at their tops.