Entitled: "Disciplina militar de, catapulta machina de guerra de las antiguas"; taken from Discours sur la religion des anciens Romains by Guillaume du Choul, 1579. A Springald, or espringal, is mechanical artillery device for throwing large bolts and less commonly stones or Greek fire. It was constructed on the same principles as a Greek or Roman ballista (an ancient missile weapon that launched a large projectile at a distant target), but with inward swinging arms. It was also known as a skein-bow, and was a torsion device using twisted skeins of silk or sinew to power two bow-arms.