15. Castle Defenders vs Attackers
Catapults relied on torsion or tension to store energy prior to release. By contrast, trebuchets relied on gravity: a heavy weight on one side of a pivot, with a long arm from which a stone was flung on the other side. Trebuchets were faster and easier to construct, and used relatively few expensive materials, such as the pricey elastic ropes needed for torsion catapults. On the downside, trebuchet ranges were shorter than those of torsion catapults. However, trebuchets made up for that with consistency. Torsion catapults were not consistent, with factors such as rope dampness or loss of elasticity causing the impact ranges to vary. Trebuchets by contrast relied on the constants of gravity and a fixed weight for energy. Once ranged in, they would hit the same spot if given the same weight projectile.
Tunnels were often used to defeat castles and other fortifications. Tunneling was particularly effective against walls that were not built atop solid rock. Besiegers would dig beneath the walls either to bypass them and allow attackers to emerge on the other side, or to undermine and collapse the walls. When undermining the walls, besiegers would tunnel until they got beneath the foundations of a wall section. As they excavated a space beneath the foundation, they would use temporary wooden props to keep the walls up. Once a sufficiently large space was dug beneath the walls, the besiegers would burn the props, causing them to collapse, along with the section of wall above them. The defenders, always on the lookout for such attempts, often dug counter tunnels in an attempt to intercept and destroy the underground attackers.
