Leonardo da Vinci’s giant crossbow was a giant bow mounted on a wheeled platform for warfare.
The design was intended to magnify the destructive power of a crossbow by making the bow vastly larger than a person could carry. Its wheeled carriage supported the weapon and allowed it to be positioned, while a mechanical winding system supplied the force needed to pull back the string.
Leonardo presented the concept as part of military engineering for the Milanese court. The weapon’s scale is the memorable feature, but the design also shows practical attention to loading, transport, and stability. It was a proposal, not a confirmed battlefield system.
The answer is still “giant crossbow,” not ballista. Ballistae were ancient missile weapons that usually used twisted cords to power their arms, whereas Leonardo’s drawing preserves the basic bow-and-string arrangement of a crossbow.