What Leonardo da Vinci siege weapon had a giant bow mounted on a wheeled platform?

Leonardo da Vinci’s giant crossbow was a siege weapon with an enormous bow mounted on a wheeled platform.

Leonardo designed the weapon around 1488–1489 while working in Milan. His drawings show a broad bow, a long stock, and wheels intended to help move the machine. A winding mechanism would have drawn the bowstring back, allowing the weapon to launch a large bolt or other projectile.

The design emphasized intimidation as well as range. Leonardo’s notes describe a bow approximately 42 braccia wide, although the exact modern conversion of a braccio varies. The machine was probably never constructed for battle, and surviving evidence does not show that it was tested successfully.

It is often confused with a classical ballista because both use tension to launch projectiles. Leonardo’s machine, however, is specifically a giant crossbow: it uses a bow and string rather than the torsion bundles characteristic of many ancient ballista designs.