What siege weapon did Leonardo da Vinci design with a giant flexible bow?

Leonardo da Vinci designed a giant crossbow as a siege weapon.

Leonardo’s giant crossbow was drawn during his Milanese period, probably in the late fifteenth century. The weapon had an enormous bow mounted on a broad wheeled frame. Its size was intended to create a powerful psychological effect as well as to launch a large projectile.

The design included mechanisms for drawing the bow and wheels for moving the weapon. Leonardo’s notes show his interest in making the machine stable and practical enough for military deployment. Its scale distinguished it from an ordinary handheld crossbow.

The giant crossbow was never a standard battlefield weapon and is known from drawings rather than surviving military use. It is also sometimes mislabeled as a ballista, but a ballista is a different ancient torsion-powered weapon. Leonardo’s design used the characteristic bow-and-string arrangement of a crossbow.