High Quality Content by WIKIPEDIA articles! A siege tower (or in the Middle Ages a belfry) is a specialized siege engine, constructed to protect assailants and ladders while approaching the defensive walls of a fortification. The tower was often rectangular with four wheels with its height roughly equal to that of the wall or sometimes higher to allow archers to stand on top of the tower and shoot into the fortification. Because the towers were wooden and thus flammable, they had to have some non-flammable covering of iron or fresh animal skins. The siege tower was mainly made from wood but sometimes had metal parts.