The BallistaThe Roman engineers wanted a bigger machine with a greater range, so in 50 b.C., they invented the ballista. The ballista was, unlike the Greek Catapulta, built almost entirely out of wood. The ballista used an older spring frame type that was more powerful as the arms could travel further, but it was also more expensive so it was used primarily for big stone throwing machines. The ballista also had the ratchet device on the outside, made out of steel. It was larger than the catapulta, in fact, some of the machines were the biggest ever made in the Roman period! They were also very expensive, because of the size and of the older, but more powerful spring frame.