Leonardo da Vinci’s giant crossbow used a curved bow frame and was intended to launch a single massive projectile.
The design enlarged the familiar crossbow into a siege-scale weapon. Leonardo added a sturdy supporting frame and mechanical equipment so that the bow could be drawn despite its great size. Its broad structure may also have been intended to improve stability and increase the visual impact of the weapon on a battlefield.
Leonardo produced military designs for powerful patrons who valued both engineering innovation and psychological effect. The giant crossbow is one of his clearest examples of transforming a known weapon through scale and mechanism. There is no reliable evidence that this exact design was manufactured and used in combat.
This question concerns the same invention often called Leonardo’s crossbow, not his organ gun. The organ gun carried many barrels for volleys, while the giant crossbow centered on one oversized bow and one main projectile. Ancient catapults also launched large missiles but used tension, torsion, or counterweight mechanisms rather than a crossbow string.