A ballista is a stationary ranged weapon that is in many respects similar to a crossbow. They were made in all sizes and forms, but they all share the same function: launch bolts at the enemy. They get their power from torsion coils, which the arms of the bow are attached to, and most often they have a winch for winding up the weapon.
|Sketch of an ancient ballista|
|Isometric view, with the string drawn|