Derived from the Greek for "shield breaker", catapult has become, more or less, a generic term for every piece of pre-gunpowder artillery that isn't a ballista. Specifically, it usually indicates a stone-throwing device1 which is occasionally loaded with other forms of ammunition as required.
Obviously this definition covers a lot of ground - not to mention a large number of different mechanisms. Common designs included:
- Beam Engine: Broadly a great big centerpoise lever, firing the missile from one end by the force of a large number of men (or other animals) pulling very hard on the other. A fairly primitive design and quickly superseded.
- Torsion Engine: These used the energy stored in a spring, a bundle of twisted fibre or something similar to drive the throwing arm. Required a signficant level of engineering to produce, but probably the user's best bet when a mobile piece was required. Examples would include the onager and springald.
- Counterweight Engine: A counterpoise lever, similar to the beam engine but using the mass of a large counterweight to supply the driving force - the counterweight is hoisted into the air and allowed to drop, driving the end of the arm holding the missile up as it falls. Potentially extremely powerful, but tended to also be immobile once set up for reasons of stability. The trebuchet is probably the best example of a counterweight engine.
Limits to the mobility of most designs of catapult made them more suited for siege work than for battlefield use - some ancient armies made good use of them in the field, but for most of the middle ages military logistics was so poor as to make them impracticable. By the time they might have been deployable, they were already being rapidly superseded by cannons.
The name is also used to refer to a slingshot (especially in the United Kingdom).
Game and Story Use
- These should be prominent players in any siege in the pre-gunpowder era. Their shipping (as dissassembled kits in some cases), placement and assembly are all worthwhile story points - and landmarks in the siege. Once they are assembled (especially in the case of the larger trebuchets) the intended breach site is obvious and cannot be easily changed - special operations to destroy the emplaced weapons, or preparations for an impending breach - also provide opportunities.
- By medieval standards these a complicated devices and finding a competent siege engineer may be something of a challenge. Such an individual may very well be a mercenary and will definitely be a target for assasination or subversion.