The tradition dates the first mechanical artillery to Syracuse under Dionysius I around 399 BCE: the gastraphetes, a large crossbow braced against the belly to span it. It stored energy in a bent bow and was limited by what wood and horn could take.
The decisive development was torsion, which stores energy in twisted skeins of sinew or hair rather than in a bending stave. Torsion engines could be scaled up, and by the Hellenistic period engineers worked to calibration formulae relating the diameter of the spring-hole to the weight of the projectile — the earliest known engineering design rules of their kind.
Two families resulted: bolt-shooters for anti-personnel and precision work, and stone-throwers for battering. Roman armies carried both, and Vegetius reports artillery attached at legion and cohort level, though his numbers belong to a period he does not specify.
What the evidence supports
Torsion artillery was calibrated by formula.
Philon and Heron transmit design rules relating spring diameter to projectile weight. This is unambiguous evidence of systematic engineering practice.
Artillery components have been excavated.
Metal spring-washers, frame fittings and large numbers of bolt heads and stone shot are known from military sites; stone shot at siege sites can sometimes be matched to engine sizes.
Vegetius's establishment figures cannot be dated.
His account of artillery per unit is often quoted as 'the Roman practice'. He is a late compiler drawing on sources of different periods and does not say which he is describing.
Terms
- gastraphetes
- 'Belly-bow'. The earliest mechanical artillery, spanned against the abdomen.
- ballista / catapulta
- Roman terms whose reference shifts over time; by the late empire the usage has effectively swapped.
Primary sources
Philon of Byzantium, Belopoeica
A Hellenistic technical treatise on artillery construction and calibration.
Heron of Alexandria, Belopoeica
A later technical treatise transmitting the design formulae.
Vitruvius, On Architecture 10
Roman artillery described by a practising military engineer.
Battles
52 BCE
Alesia
Caesar besieged Vercingetarix inside a hilltop stronghold while simultaneously defending his own siege lines against a relief army, and ended organised Gallic resistance.
How to read the evidence labels
- Evidence level: Documented
- Supported by a named primary text or by excavated material evidence.
- Evidence level: Probable
- Supported by strong inference that most specialists accept.
- Evidence level: Disputed
- Substantial specialist disagreement exists; competing readings are stated.
- Evidence level: Literary
- Belongs to poetic or mythological construction rather than to history.
- Evidence level: Mythological
- Belongs to shared religious or mythic tradition rather than to any single text.
- Evidence level: Unknown
- The available evidence is insufficient to decide.
These labels describe the status of the evidence, not our confidence in a conclusion. A claim marked Literary is not a claim we doubt; it is a claim about what kind of thing a poem is.