Pompeii’s archaeological excavations have primarily centred on the severe eruption of Mount Vesuvius during AD 79; however, new investigations have shifted the spotlight to a violent chapter nearly 170 years earlier. Using advanced laser scanning and 3D digital imaging, Adriana Rossi, the lead researcher and team, discovered various unique and identifiable ballistic signatures on the town’s northern fortification walls. According to research published in MDPI, the presence of these specific patterns suggests the use of the polybolos (a multiple-shot or repeating catapult), which has been described as the equivalent of an ancient machine gun, in the siege of Pompeii. The polybolos exemplified a revolution in chain-driven projectile launching from Hellenistic engineering and dramatically advanced siege warfare in the Roman world.
Discovery of an ancient weapon, the ‘machine gun’, at Pompeii
Evidence for this ancient weapon, the ‘machine gun’, does not come from any physical parts but rather from the ‘ballistic scars’ on the limestone walls of Pompeii. Researchers found that the curved and tightly clustered impact craters were much different from the large, separate craters made by standard heavy catapults. These impact marks were in the same arc-shaped clusters, indicating that an object was being fired from a stationary position and that the respective recoil or hand-firing correction could cause a straight line of fire. It also shows that during the period of the Social War (89 BCE), there was damage created by Roman General Lucius Cornelius Sulla when he besieged Pompeii, as noted in the research ‘From Pompeii to Rhodes, from Survey to Sources: The Use of Polybolos’. General Sulla had most likely gained access to this technology through his campaigns in the Eastern Mediterranean and therefore was able to defeat Pompeian defenders.
The revolutionary mechanics of the polybolos
The polybolos was a masterpiece of engineering created in the third century BC by Philo of Byzantium. This device differed from traditional ballistae in that, rather than requiring manual tensioning with every shot, it could continuously reload and fire until its magazine was exhausted. It utilised a flat-link chain (considered to be the earliest known use of this type of mechanism in the world), which was attached to a windlass.The operator of the polybolos used a handle to turn the windlass, while, at the same moment, being able to draw the bowstring, drop another bolt from the gravity-fed feeding tray into position for firing and release the firing mechanism, all with a single motion. Because of the design of the polybolos, one battery of polybolos could provide effective suppression of defenders located on city walls and clear a defensive position on a parapet with a rapid stream of projectiles.
How high-tech scans identified the polybolos
The research team used high-resolution LiDAR (Light Detection and Ranging) and digital photogrammetry in order to differentiate types of artillery damage from natural erosion. Researchers were able to measure the depth, diameter, and trajectory of each hole by creating an extremely dense three-dimensional LiDAR point cloud of the wall surface. The polybolos impacts were remarkably uniform, suggesting they were fired from the same (and therefore mechanically consistent) machine rather than different (and therefore mechanically inconsistent) humans. The pattern of the artillery marks indicates to the research team that the polybolos were likely fired from elevated wooden towers designed to fire down onto the Pompeian defenders. This probably explains the concentration of clusters of artillery impacts at very high elevation points along the northern fortifications.
