Leonardo da Vinci’s giant crossbow was a weapon design intended to launch very large projectiles.
Leonardo drew the weapon around 1488–1490 while working on military designs for powerful patrons. The sketch shows an enormous bow mounted on a wheeled frame. A mechanical winding system was intended to draw the bowstring back, because a bow of that size could not be pulled by ordinary human strength.
The design was meant to create psychological impact as well as physical force. Its huge scale would have made it intimidating, even though there is no reliable evidence that Leonardo’s exact machine was built and used in battle. The drawing is therefore best treated as an ambitious engineering proposal.
A giant crossbow is different from a ballista, which is a distinct ancient torsion-powered weapon, and from a catapult, which usually throws objects with an arm. Leonardo’s design retained the bow-and-string principle while greatly enlarging it.