The torsion power ballista is said to be created in 338 - 326 B.C in Greece. They allegedly invented screws/nails, rotary mills, screw press, bronze casting techniques, water clock and the torsion catapult. Some of the challenges that the builders would have faced would be that they cut their own tree’s up using axe’s and saws in which it means that you won’t get the best of cuts. Also the fact that if they didn't have trees around them they would have to drag them along to battles. Also the fact that they wouldn't generally have a building book with them so they would have to go off memory so that means that everyone would have to learn how to build them or otherwise they would have dedicated engineers. Well “drills” which where hand operated by turning them in a clockwise rotation, a saw which is used to cut a tree down is used by a movement of the blade on the tree by the movement of a hand. And then the nails/ dowels where just hammered in to achieve maximum strength due to it being a tight slot that it has to slide into.

Favourite bibliography links:

https://en.wikipedia.org/wiki/Torsion_siege_engine