Ballista (Stone Thrower)Concepts found in the catapult and the bow were combined to design the ballista. Rope springs were set in the frame angled to each other in the form of a "V", which increased the power. A very sturdy frame accommodated the extra torque, which meant extra weight, and less maneuverability. Note that the wood disk at the base of the ratchet pulls has holes evenly spaced along the circumference, allowing the ratchet pulls to be lifted out and into the next hole. Making quick work of pulling back the release pin and the loaded stone.
This design was one of three incarnations of this type of weapon.
The Scorpio (Dart Thrower) circa 50 BC, fired a 27 inch bolt. It had a wooden construction, and its bow arms were curved to help increase the amount of twist in the rope, and therefore greater range.
The Cheiroballistra, circa 100 AD, was a major improvement over the scorpio. It was sturdier than its predecessor (the Scorpio), it was lighter than the Ballista, and it had a greater range. The frame was made of metal which allowed the rope springs to be spread farther apart which made it more powerful, and also had the added benefit of making it easier to sight the target. The springs were encased in bronze cylindrical sleeves to help protect them from the weather. A modern reconstruction of the Cheiroballista was built and tested. It was proven to be a very accurate weapon.
The main advantage of any of these weapons was that they could be built quickly and were easily handled by two men.