1) Ancient Greek artillery 2) Projectile weapon 3) Torsion artillery 
Carroballista was an ancient, cart-mounted ballista, a type of mobile field artillery. According to the Roman author Vegetius (Epitoma rei militaris II.25), each legion had 55 carroballistae (one per century) which were arrow/bolt-shooter of the cheiroballistra type. Vegetius tells us that each carroballista was carried by mules and operated by on...
Torsion artillery.