Before Greek engineers in the 4th century BC, no Western army had a weapon that stored mechanical energy beyond what a human could pull and hold by muscle alone. After them, the next eighteen centuries of artillery design would consist of refinements on what they had built. The gastraphetes, the oxybeles, the lithobolos — the line of descent runs unbroken through the Roman scorpio and ballista to the Byzantine torsion engines that were still in use during the early Crusades.
Gastraphetes
The "belly-bow" — the proto-crossbow developed in Syracuse around 400 BC, traditionally credited to engineers working for the tyrant Dionysius I. A composite bow mounted on a wooden slider, drawn back by the user pressing his stomach against a curved butt-plate to load the weapon against his body weight. Range was perhaps 200 yards; accuracy at that distance was reportedly impressive for the period.
The gastraphetes did not see widespread adoption — it was bulky, slow to load, and limited to specialized siege use — but its conceptual significance was enormous. It established the principle that mechanical advantage could store energy beyond human draw strength, and it was the immediate ancestor of every torsion artillery weapon that came after.
Oxybeles
The first true torsion artillery: a two-armed bolt-thrower powered by tightly twisted bundles of sinew or hair rather than a flexed bow. Developed by Macedonian engineers under Philip II in the mid-4th century BC, the oxybeles could throw heavy iron-tipped bolts to ranges exceeding 300 yards with a force capable of driving through shield, armor, and the man behind both.
Alexander used oxybeles extensively in his sieges, most famously at Tyre in 332 BC. After his death, Hellenistic kingdoms refined the design and produced detailed engineering treatises. When Rome later inherited the technology from defeated Hellenistic armies, the Roman scorpio was essentially a slightly-refined Greek oxybeles — the form persisted through the Roman Empire and into the Byzantine period.
Lithobolos
The stone-throwing torsion artillery of the Hellenistic kingdoms — the same two-armed mechanism as the oxybeles, scaled up to throw stones rather than bolts. Hellenistic engineers developed a classification system for these weapons by stone-weight, ranging from small 3-pound throwers up to massive 1-talent (57-pound) siege pieces capable of breaking masonry walls.
All three major Hellenistic kingdoms — Seleucid, Ptolemaic, and Antigonid — built and used lithoboloi in numbers. The siege of Rhodes by Demetrius Poliorcetes in 305–304 BC featured massive numbers of these weapons on both sides. When Rome later defeated the Hellenistic kingdoms, the Roman ballista was simply a Latinized version of the lithobolos, with refinements in metal-frame construction. The form lasted, under Greek-derived names, for nearly a millennium afterward.