I would fully expect them to do so. So...Ballistas would attack the guys getting close to them until those guys finally made it up close and killed the ballista. That's exactly how it SHOULD be. BUT! Why would a ballista (lets say after the troops have tried to come out and kill them yet the ballista killed them all before they got to them) walk right up to the wall and station themselves under a rockfall instead of continuing to attack from afar until they have killed the people manning the rockfalls? or destroyed the wall entirely?

