Here’s what you’ll learn when you read this story:

Researchers have uncovered evidence that a weapon known as the polybolos—or multi-thrower—was used during the Roman conquest of Pompeii.

Originally invented in classical-era Greece, the weapon used a chain-drive to fire darts rapidly.

Although no physical example of the device has been found, the Mount Vesuvius eruption buried Pompeii less than 200 years after Roman troops conquered the city, preserving the polybolos marks.

This story is a collaboration with Biography.com.

Mysterious damage patterns on a 2,000-year-old fortress are rewriting what we know about Roman firepower.

If the ancient world had its own version of a machine gun, it may have left its calling card embedded in the stone walls of Pompeii—and researchers think they’ve finally found it.

A team led by Adriana Rossi of the University of Campania has identified a distinctive pattern of damage along the northern stretch of Pompeii’s fortified walls that they believe was made by a polybolos—a Greek-engineered mechanical dart-thrower capable of firing multiple projectiles in rapid succession. The marks, they argue, date to the Roman siege of the city in 89 B.C.E., led by the forces of general Lucius Cornelius Sulla. Less than 200 years later, the eruption of Mount Vesuvius buried Pompeii under meters of ash and pumice, preserving those battle scars in near-perfect condition for modern scientists to find.

The evidence is striking. Tight, radial clusters of quadrangular cavities arranged at short, regular intervals along curved lines appear on the fortress walls near the gates of Vesuvius and Herculaneum. The shape and spacing of the indentations match the profile of military darts from the period—and nothing else in the known Roman arsenal fits the bill. To build their case, Rossi’s team deployed an impressive suite of modern imaging tools: close-range photogrammetry, structured-light 3D scanning, and laser scanning, all working together to produce high-resolution 3D models of each impact site. Their findings were published in the journal Heritage.

But what exactly is a polybolos—and why has it captured the imagination of historians for centuries?

The weapon is believed to have been invented by Dionysius of Alexandria, a Greek engineer who worked in the famous arsenal of Rhodes around the third century B.C.E. His design was a mechanical marvel for its time: a torsion-powered device featuring a chain drive and gear system that automatically loaded bolts into firing grooves, allowing it to launch projectiles in rapid, repeating bursts. Think of it as the ancient world’s closest analog to a belt-fed machine gun. The polybolos was described in detail by the Greek writer Philo of Byzantium, whose third-century B.C.E. text remains the primary historical source on the weapon. There’s just one catch—no physical example of a polybolos has ever been found. It exists, so far, only in words and, perhaps now, in stone.

That’s precisely what makes the Pompeii discovery so significant. Rossi’s team is now cross-referencing the physical damage patterns with Philo’s written descriptions to determine whether they can reconstruct a working 3D virtual model of the weapon. The researchers note that “assembling the components of the polybolos in accordance with Philo’s treatise will enable a more in-depth exploration of its technical specifications”—potentially filling in centuries of blanks about how the device actually functioned in the field.

If the team’s hypothesis holds, the walls of Pompeii hold a rare, tangible record of cutting-edge military technology in action—a snapshot of Roman legions deploying what may have been the most sophisticated rapid-fire weapon the world had ever seen. The city that Vesuvius froze in time may have been quietly holding this secret for over two millennia, waiting for the right combination of lasers, algorithms, and curiosity to finally read it.

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