This is not a ballista. As far as I can tell this is not anything that has ever existed. There were bow-based catapults called ballistae, but they didn't have a swinging arm. And there were swinging arm catapults called onagers, but they were not powered by a bow.
This is not a ballista. As far as I can tell this is not anything that has ever existed. There were bow-based catapults called ballistae, but they didn't have a swinging arm. And there were swinging arm catapults called onagers, but they were not powered by a bow.