The ballista , plural ballistae, was an ancient missile weapon that launched a large projectile at a distant target. Developed from earlier Greek weapons, it relied upon different mechanics, using two levers with torsion springs instead of a prod (the bow part of a modern crossbow), the springs consisting of several loops of twisted skins.

Early versions projected heavy darts or spherical stone projectiles of various sizes for siege warfare. It developed into a smaller sniper weapon, the scorpio, and possibly the polybolos. many skill-Up mechanisms and scientific  knowledge are applied in catapults, so children can grab many skills and physic knowledge in this product (Skill-Up Toy). they are able to build own catapult, then they can play several game via this Ballista