A crossbow is a mechanical weapon used for firing bolts or arrows. It usually consists of a groove in which a projectile is inserted, and a string which is drawn tight and held by a trigger. When the trigger is released, the projectile fires.
In Redwall, Constance and the Beaver constructed a giant crossbow in an attempt to assassinate Cluny the Scourge. They used a large table as a base, and instead of yew wood, they used a sapling from the orchard. Instead of an arrow, the two used an old candle snuffer with the end flattened to a point. Their plan was to fire their weapon into a tent occupied by Cluny. However, they mistook Cheesethief for the rat and killed him.
In The Rogue Crew, Braggio Ironhook built two giant crossbows, and had them fitted to the prow and stern of the wheeled ship Greenshroud. After Braggio's death, Razzid Wearat used the weapons to slay several defenseless woodlanders, and knocked open Redwall Abbey's main gates by firing one of the enormous crossbow bolts.