I can't wait to see the TG Roman Catapult! Catapult is generic term referring to all pre-gunpowder artillery. The question is will the TG Catapult be a Ballista; which no one has done accurately yet, or an Onager? The Roman Onager should not have wheels as they were assembled onsite not towed. Also the Roman Onager utilized a sling to fire shot, not a cup. Power was provided by torsion springs made from twisted sinew or horsehair. Tension Catapults used laminated wood bows and were a Medieval invention, as the torsion spring technology was lost in the West with the fall of Rome. The greatest Medieval artillery was the Trebuchet; which was a Chinese invention conveyed to the west via the Arab conquests. The Trebuchet counterpoise Catapult could lob a 300 pound stone 300 yards and breach walls. A large Roman Siege Ballista could fire a 60 pound stone over 400 yards in a flat trajectory and breach walls or destroy parapets.
Amazing technology for the period!