Ballista

The ballista (Latin, from Greek βαλλίστρα - ballistra and that from - βάλλω ballō, "throw"), plural ballistae, was an ancient missile weapon which launched a large projectile at a distant target.

Usage
Developed from earlier Greek weapons, it relied upon different mechanics, using two levers with torsion springs instead of a prod, the springs consisting of several loops of twisted skeins. Early versions ejected 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.

Role in Astro Knights
A ballista is seen on the Castle. It was used by the Royal Guards during the Battle of Arturus.