Today in the modern world we have all the technology to us we can build anything g we can build buildings that  a really tall we can build weapons that shoot out bullets that go really far and we have technology such as laptops phones and Ipods we have a lot of good technology but back in 400 bc the people back the had none of that they didn't have screens laptops and computer or none of that all they had to build stuff is pretty much wood cause wood back then was the only source of technology that people could afford so you could imagine the people trying to building ballista it was a very tough challenge for them to build because all the equipment they would have in 400 bc is the time where all they had is hammers made out of wood everything was wood and wood wasn't an easy thing to find overall I think that building the ballista