What military device did Leonardo da Vinci design as a giant crossbow?

Leonardo da Vinci designed a giant crossbow as a large military weapon intended to launch heavy bolts.

His drawing shows an enormous bow mounted on a wheeled frame. Leonardo proposed using a mechanical system to draw back the bowstring, since the bow was too large for a person to span by hand. The design also included a broad base and wheels intended to improve stability and mobility.

The giant crossbow belonged to Leonardo's work on military engineering for powerful patrons in Renaissance Italy. It is often described as an intimidating design, but there is no reliable evidence that Leonardo's full-scale version was built and used in battle. The surviving image is a design study, not a battlefield report.

It is easy to confuse the weapon with a catapult or ballista. A crossbow stores energy by bending a bow and releases it through a string; catapults and related engines generally throw projectiles from an arm or sling.