Ballista n. : An ancient military engine, in the form of a crossbow, used for hurling large missiles.

Example:
What is the physics behind a Ballista catapult?

Taxonomy
weapon, Roman ballista, ballistae, Roman, Greek, reconstructions, projectiles, artillery, torsion springs, the Roman, Roman Weapon, Manuballista, Britain, Empire, the Roman Empire, lighter, torsion, battlefield.

Defination from the web:
Ballista which had by now spread to several cities around the Mediterranean, all of which became Roman ... The ballista's relatively lightweight bolts also did not have the high momentum of the stones thrown by the later onagers, trebuchets, or ...