Ballista, or BALISTA (Gr. ballein, 'to throw'), a Roman military engine, resembling a huge bow, which, like the catapulta and the onager, propelled large and heavy missiles, chiefly through the reaction of a tightly-twisted rope of hemp, flax, catgut, sinew, or hair, or else by a violent movement of levers. Numerous weapons of an analogous character were known in the middle ages—such as the mangonel; the trebuchet, the robinet, which threw darts as well as stones; the tricolle, which hurled quarrels, or square-headed arrows; the espringal or springal, which threw large darts, &c. The Arbalest, or Crossbow (q.v.) may be regarded as a small portable arrow-throwing ballista.