What large siege weapon did Leonardo da Vinci design with a flexible bow and six wheels?

Leonardo da Vinci designed a giant crossbow with a flexible bow and six wheels.

The drawing shows an oversized crossbow intended to launch a large projectile. Leonardo’s design included a broad bow, a stock, a loading mechanism, and a wheeled support structure. The wheels were not simply decorative: they helped the machine move and were part of the engineering solution for handling its large size.

Leonardo appears to have aimed for intimidation as well as destructive power. The weapon’s scale would have made it visually impressive, but a giant bow also created serious problems involving material strength, tension, aiming, and reloading. There is no reliable evidence that this particular design was built and used in combat.

The invention is often confused with a ballista or catapult. Those weapons use different mechanisms. Leonardo’s machine is classified as a crossbow because it stores energy in a bent bow and releases it through a string to propel a projectile.