Warmatrix

War Matrix - Ballista

A ballista is a heavy bolt or stone thrower, so heavy that it is ranked among artillery, rather than handweapons. It was a development of the siege crossbow like the Greek oxybeles, however its firing mechanism was different. Instead of working by tension, stretching a single string, the arms of a ballista were encased in ropes or sinews and tension was built up by torsion. This tension had to be applied with levers or a winch, because the tension strength was more than a man can handle. When released, the string fired a projectile in a straight line. Some ballistae fired large bolts or javelins, others stones or even decapitated heads.
The range of a ballista varied wildly, from as little as a few dozen meters to more than a kilometer, depending on its firepower and the type of ammunition loaded. A ballista was much more powerful than a crossbow; a large one could shoot javelins of up to 5 kilograms. It was known to have pierced several rows of men and shields with a single shot. A weakness of torsion-powered siege engines was that the ropes or sinews tend to slack in wet weather. Also, each shot caused wear and tear, so the machine demanded a lot of maintenance.
The Chinese and Greeks invented ballistae more or less simultaneously, around the 7th - 4th century BCE. A well-known Greek example is the "lithobolos", stone-thrower. The Romans used portable ballistae called scorpions in the Second Punic War. They also employed carroballistae, mounted on carts so that they could quickly be maneuvered into position. In the Middle Ages a spingald was used, a light ballista that was more an anti-personnel crossbow than true artillery.
Ballistae were used both in sieges and on the battlefield. In the late Middle Ages they were made obsolete by bombards, which had more power.