TLDR: The ballista was an ancient weapon that launched bolts or stones at distant targets. It was developed from earlier Greek weapons and used torsion springs to propel the projectiles. The Romans adopted and improved the ballista, using it in sieges and battles. It was a highly accurate weapon and played a significant role in the Roman Empire's military strategy.

The ballista was a type of missile weapon used in ancient times. It was developed from earlier Greek weapons and relied on torsion springs for power. Instead of using a tension prod like a modern crossbow, the ballista used two levers with torsion springs made of twisted skeins. This allowed it to launch heavy darts or spherical stone projectiles at distant targets.

The early ballistae in Ancient Greece were developed from two weapons called oxybeles and gastraphetes. The gastraphetes was a handheld crossbow, while the oxybeles was a larger and heavier construction mounted on a tripod. These early ballistae were used in siege warfare.

The Romans adopted the ballista after the conquest of the Greek city-states. They further developed and improved the weapon, making it smaller and more powerful. The Roman ballistae were made of wood, with iron plates and nails for reinforcement. They had a slider on top for loading bolts or stones, and a pair of winches and a claw for tensioning the bowstring.

The ballista was a highly accurate weapon, capable of hitting individual soldiers on the battlefield. However, its range was limited, and it was most effective at shorter distances. The Romans continued to use the ballista in their military campaigns, including Julius Caesar's conquest of Gaul and his campaigns in Britain.

During the decline of the Roman Empire, resources for building and maintaining complex machines like the ballista became scarce. The weapon was gradually replaced by simpler and more efficient siege engines like the trebuchet and mangonel. However, the ballista still saw some use in medieval siege warfare, particularly by city and castle garrisons.

In conclusion, the ballista was an ancient missile weapon that played a significant role in the military strategies of both the Greeks and Romans. It was a highly accurate and powerful weapon, used in both siege warfare and on the battlefield. While it eventually fell out of use with the rise of more advanced siege engines, the ballista left a lasting impact on military technology.