It was constructed on the same principles as an Ancient Greek or Roman ballista, but with inward swinging arms and threw bolts instead of stones.[1] The springald was a defensive bolt thrower based on the torsion mechanism of ancient ballistas, with two arms held in a skein of twisted sinew or hair.According to digital models and projections, a springald could throw a bolt around 180 meters if mounted on a tower at an elevation of 15 degrees.Springalds were commonly used to defend gates from atop towers, where their skeins were safe from wet weather and their bolts could be shot a greater distance.Springalds were expensive to produce: Liebel's calculation for the cost of machines built for the pope at Avignon puts them at six months' wages for an unskilled laborer.
