What siege weapon did Leonardo da Vinci design with an exceptionally large bow?

Leonardo da Vinci’s exceptionally large siege weapon was a giant crossbow.

Leonardo designed the weapon in the late fifteenth century, when Italian states competed to improve artillery and siege technology. His drawing shows a very large bow mounted on a wheeled frame, with a loading mechanism intended to draw the bowstring back mechanically.

The design was probably meant to launch a large projectile and to create a dramatic psychological effect as well as physical damage. Its size made it unsuitable for being drawn by human strength alone, so the machine incorporated mechanisms to reduce the effort required to cock it.

The giant crossbow was a concept, not a documented battlefield success. It is often confused with ancient torsion weapons such as the ballista, but Leonardo’s design used a large flexible bow and mechanical loading equipment. His military notebooks contain many such proposals without proof that every one was constructed.