Over 150 years before Pompeii was famously frozen in time by the eruption of Mount Vesuvius, the city was drawn into the Social War (91–88 BC). This conflict broke out when Rome's Italian allies, long bound to the Republic but denied full citizenship, revolted in a bid for political rights and autonomy. In 89 BC, Roman general Lucius Cornelius Sulla laid siege to Pompeii, deploying advanced Roman weapons and artillery against its defenses to break resistance. The northern walls, between the Vesuvio and Ercolano gates, were particularly vulnerable due to the gently sloping terrain that made them easier to assault than the southern side, which was naturally protected by a steep drop toward the sea.
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Comparison between a 1925 photo (Van Buren) and a 2024 photo highlighting circular ballistic marks on Pompeii's northern walls (Rossi et al., Heritage / CC BY 4.0)
Deciphering the Fan-Shaped Impact Patterns
Two thousand years later, Pompeii's northern walls still bear the marks of Sulla's siege. While traditional catapult damage left large, circular craters from heavy stone balls, researchers noticed something far more unusual between the Vesuvio and Ercolano gates. Clusters of small, four-sided indentations are arranged in tight, fan-shaped patterns along the tufa ashlars of the ancient fortifications.
According to the study published in the journal Heritage by researchers from the University of Campania and the University of Bologna, these distinctive marks bear no resemblance to the circular impact signatures expected from ballista stones or whistling sling projectiles. Instead, their geometry, spacing, and radial orientation point to multiple projectiles fired in rapid succession along nearly identical trajectories. According to the research team, these patterns perfectly match the mechanical sweep of a polybolos — a repeating dart-throwing weapon whose invention is attributed to Dionysius of Alexandria and whose mechanisms are described in detail by Philo of Byzantium in the 3rd century BC.
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Scale comparison of two detailed textured mesh models: on the left, (A) ballistic impact of a spherical stone projectile; on the right, (B) fan-shaped groups of smaller quadrangular impacts. Survey, 3D models, and rendering by S.B. (Rossi et al., Heritage / CC BY 4.0)
The Polybolos: An Ancient Rapid-Fire Marvel
The polybolos, whose name means "multi-thrower" in Greek, was a torsion-powered repeating ballista invented by Dionysius of Alexandria, a Greek engineer who worked at the Rhodes arsenal in the 3rd century BC. Unlike standard catapults, the polybolos featured a wooden hopper magazine capable of holding several dozen bolts and a mechanical chain drive — the earliest known application of such a mechanism. This allowed it to fire multiple metal-tipped darts in rapid succession without manual reloading, making it the closest thing the ancient world had to a machine gun.
A modern reconstruction of the repeating "polybolos" catapult of Dionysius of Alexandria (3rd c. B.C.), Kotsanas Museum of Ancient Greek Technology, Athens, Greece (Aga39memnon / CC BY 4.0)
Philo of Byzantium noted that the weapon was extremely effective for hitting a single target multiple times, but less useful for spreading fire across multiple enemies. He wrote: "The missiles will not have a spread, since the aperture has been laid on a single target and produces a trajectory more or less along one segment of a circle; nor will they have a very elongated dropping zone." This description aligns strikingly well with the fan-shaped patterns recorded on Pompeii's walls, where multiple impacts follow a narrow, curved arc. In 2010, the television program MythBusters built and tested a replica of the polybolos based on Philo's description, concluding that its existence as a historical weapon was entirely plausible.
Digital Archaeology Reconstructs the Siege
To investigate further, the research team used advanced 3D scanning, laser photogrammetry, and structured-light imaging to create highly detailed models of the wall surfaces. By performing reverse modeling, they worked backward from the damage to infer the shape and behavior of the projectiles. The results suggest the impacts were produced by metal-tipped darts with pyramid-shaped heads, striking at an estimated speed of approximately 109 meters per second. The dimensions closely match pyramidal dart heads recovered from other Roman military sites held in museum collections across Europe.
The placement of the impact clusters also provides new insight into how the siege of Pompeii may have unfolded. The researchers hypothesize that the polybolos was aimed at archers emerging from the bases of towers or defenders briefly exposing themselves between the merlons.
"The unequivocally radial configuration of the closely spaced impacts observed at Pompeii makes it reasonable to hypothesize the use of an automatic scorpion intended to strike archers emerging in succession from the lateral posterns of the towers," the authors write.
The marks on the walls are simply the result of missed trajectories, as the weapon was intended for anti-personnel purposes rather than demolishing the fortifications themselves.
Sulla had previously served as governor of the Roman province that included Rhodes, a renowned hub of engineering excellence in the ancient world. The authors conclude that:
"it is therefore plausible that Sulla - a politically astute and technically informed commander - could have acquired or encouraged Rhodian innovations, deploying an enhanced multi-shot engine during the siege of Pompeii between the summer of 89 and the winter of 88 BC."
The fact that Pompeii was buried by Vesuvius less than a century after the siege means the volcanic ash perfectly preserved the impacts, ensuring they were not erased by the passage of time.
Top image: Location of the study area showing Pompeii's northern walls between Vesuvio and Ercolano Gates, with the study area highlighted. Source: Rossi et al., Heritage / CC BY 4.0
By Gary Manners
References
Arnold, P. 2026. Pompeii's battle scars linked to an ancient 'machine gun'. Phys.org. Available at: https://phys.org/news/2026-03-pompeii-scars-linked-ancient-machine.html
Discover Magazine. 2026. Ancient Roman Machine Gun-Like Weapon May Have Damaged Pompeii's Walls During Siege. Available at: https://www.discovermagazine.com/ancient-roman-machine-gun-like-weapon-may-have-damaged-pompeii-s-walls-during-siege-48851
Greek Reporter. 2025. Evidence of Ancient Greek 'Machine Gun', Polybolos, Discovered in Pompeii. Available at: https://greekreporter.com/2025/05/23/evidence-ancient-greek-machine-gun-polybolos-pompeii/
Rossi, A. et al. 2026. From Pompeii to Rhodes, from Survey to Sources: The Use of Polybolos. Heritage. Available at: https://www.mdpi.com/2571-9408/9/3/96
