17. Medieval Attackers Took to Tunnels to Bring Down Castle Walls
A downside of trebuchets is that their ranges were shorter than those of torsion catapults. However, trebuchets made up for that with consistency. Torsion catapults were not consistent, because factors such as rope dampness or loss of elasticity caused 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 continue to hit the same spot if given the same weight projectile. Besiegers also dug tunnels 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 inside the castle, or to undermine and collapse its walls. When they wanted to undermine the walls, besiegers tunneled 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.