The Scorpio was a smaller weapon, more of a sniper weapon than a siege engine, being operated by only one person. The Scorpio was basically a primitive giant crossbow, a ‘catapult with bolts’, probably first invented by the Greeks, then later adopted and used on a larger scale by the Roman legions. This catapult used [...]

The onager was a post-classical Roman siege engine, which derived its name from the kicking action of the machine, similar to that of an onager (wild ass). It is a type of catapult that uses te nsional pressure, generally from twisted rope, to store energy for the shot (wikipedia.org).
I try to make that machine with [...]