What device did Leonardo da Vinci design to make a crossbow easier to operate?

Leonardo da Vinci designed a crank-operated spanning mechanism to make a crossbow easier to operate.

Leonardo’s giant crossbow drawings show a large weapon whose bow was bent with mechanical assistance rather than by the shooter’s unaided strength. A crank and screw arrangement could draw back the bowstring, while other parts stabilized the weapon and helped manage the heavy limbs.

The design belongs to Leonardo’s military-engineering work in the late fifteenth century. Its great size was intended to create a powerful projectile weapon, although the practical advantages of such a large crossbow would have come with problems of transport, loading time, and construction.

The mechanism should not be confused with the trigger. A trigger releases a cocked crossbow; the spanning mechanism performs the earlier task of drawing the string back. Leonardo’s drawings also include details for the bow, frame, and support, but they do not prove that a complete giant crossbow was manufactured and used in combat.