Roman Ballista

Ballistas were similar to giant crossbows and were designed to work through torsion. The ammunition used were basically giant arrows or darts made from wood with an iron tip. These arrows were then shot “along a flat trajectory” at a target. Ballistas are notable for their high degree of accuracy, but also their lack of firepower compared to that of a Mangonel or Trebuchet. Because of their immobility, most Ballistas were constructed on site following a siege assessment by the commanding military officer.

Developed from earlier Greek weapons, it relied upon different mechanics, using two levers with torsion springs instead of a prod, the springs consisting of several loops of twisted skeins. Early versions ejected heavy darts or spherical stone projectiles of various sizes for siege warfare. It developed into a smaller sniper weapon, the Scorpio, and possibly the polybolos.

After the time of Julius Caesar, the ballista was a permanent fixture in the Roman Army and, over time, modifications and improvements were made by successive engineers. This included replacing the remaining wooden parts of the machine with metal, creating a much smaller and lighter machine, capable of even more power than the wooden version, since the metal was not liable to snap like the wood, and which required less maintenance (though the vital torsion springs were still vulnerable to the strain).