Preserved in Glass: How Mount Vesuvius Locked This Roman’s Brain in Time

Nearly 2,000 years ago, Mount Vesuvius erupted, swallowing the nearby Roman towns of Herculaneum and Pompeii in a superheated cloud of ash, dust, and volcanic material. The environment was so hot that a team of researchers say it turned at least one resident’s brain into glass.

Not only did the individual’s once-squishy, pinkish-white organ get vitrified into a hard, sparkly black material, but the glassy remains contain preservation down to the microscopic level—that is, the Roman’s axons and neurons were preserved by the extreme conditions of the volcanic eruption. The team’s analysis was published today in Scientific Reports.

“Our comprehensive chemical and physical characterization of the material sampled from the skull of a human body buried at Herculaneum by the 79 CE eruption of Mount Vesuvius shows compelling evidence that these are human brain remains, composed of organic glass formed at high temperatures, a process of preservation never previously documented for human or animal tissue, neither brain nor any other kind,” the researchers stated in the paper.

The individual’s remains were found in a bed at the Collegium Augustalium in Herculaneum. The individual was a young male—roughly 20 years old—and the researchers say he is thought to be the guardian of the collegium, dedicated to the worship of the Emperor Augustus, who died 65 years before the eruption.

Though human brain preservation is rare in the archaeological record, it is documented. Through dehydration, saponification (essentially preservation by soap), tanning, and freezing, our most important organ is preserved in various instances in time. But vitrification—converting a material into a glasslike substance—of a human brain is not documented, because of the very specific high temperatures and rapid cooling that must occur.

The individual’s brain and its remarkable preservation was first described in 2020, but at the time researchers couldn’t understand how the vitrification happened. Now, they understand the extreme and unique conditions that produced the glass brain.

The researchers noted in the paper that temperatures of the pyroclastic flows that buried Pompeii and Herculaneum were several hundred degrees—heat that would typically destroy soft tissue.

The individual’s glassy remains were “formed by a unique process of vitrification of his brain at very high temperature, and is the only such occurrence on Earth,” the researchers wrote. “Calorimetric analyses show that the temperature at which the brain transformed into glass was well above 510 °C [950 degrees Fahrenheit], implying that the body was exposed to the passage and vanishing of a short-lived, dilute and much hotter pyroclastic flow, explaining its early fast heating and the following very fast cooling.”

The team added that the unique process caused the brain and its microstructures to perfectly preserve. Indeed, analysis of the glass using a scanning electron microscope revealed neurons, axons, and other neural structures. It’s strikingly similar to the processes by which researchers are revealing writing on scrolls carbonized by the eruption of Vesuvius—also found in a Herculaneum villa.

The researchers also posit that the brain specifically was in a unique position to be preserved—as the individual’s skull and spin protected the organ from the brunt of the intense pyroclastic flow. Though extremely hot and obviously fatal, the first wave of heat from Vesuvius’ eruption wasn’t the kind of messy deluge of lava for which volcanic eruptions are known.

If you really want to tear into someone, perhaps it’s time to abandon “your ass is grass.” Instead, try “your brain is glass.”