|A photo of a recreated Roman ballista-type 'Scorpion' catapult. In essence it's much the same, but smaller than a basic 'ballista'. However, this machine was devised as a piece of field artillery. Unlike the full-sized ballista which was a siege engine firing stone balls, the scorpio supported Roman infantry on the battle field by firing bolts at enemy.
Above is a reconstructed, complete scorpio of the Ermine Street Guard in the UK (Legio XX Valeria Victrix), on display at Birdoswald Fort (Hadrianís Wall) in May 2007.