The cheiroballistra (Greek) or manuballista (Latin), which translates in all its forms to 'hand ballista', was a late Roman siege engine. Designed by Hero of Alexandria and mostly composed of metal (the spring mechanism and the skeins), it fired bolts that were smaller than those in other forms of ballistae and generally made of metal. It was the next major improvement after the scorpio. The name of the weapon implies that portable versions might also have existed, similar to crossbows.