The carroballista was a cart-mounted version of the weapon. There were probably different models of ballista under the "cheiroballistra" class, at least two different two-wheeled models and one model with four wheels. Their probable size was roughly 1.47 m width, i.e., 5 Roman feet. The cart system and structure gave it a great deal of flexibility and capability as a battlefield weapon, since the increased maneuverability allowed it to be moved with the flow of the battle. This weapon features several times on Trajan's Column.