The eruption of Mount Vesuvius in 79 C.E. is one of the most infamous natural disasters in history, burying the Roman cities of Pompeii and Herculaneum under layers of volcanic ash and debris. While the event destroyed these settlements, it also preserved them in astonishing detail, from frescoes to ancient scrolls and even the shape of the victims’ bodies.
Among the most extraordinary discoveries from this catastrophe is the case of a young man whose brain and parts of his spinal cord were transformed into glass. Scientists had never seen anything like this before and have yet to find another example.
“When we realized that there was really a glassy brain, the scientific question was: How is it possible?” says Guido Giordano, a geologist and volcanologist at Roma Tre University in Italy.
A new study published in Scientific Reports offers an explanation for this rare phenomenon known as vitrification. The researchers propose that an extremely hot ash cloud quickly heated and then rapidly cooled the man’s brain, turning it into glass.
The Discovery of the Glass Brain
The remains of this individual were found in the 1960s inside the College of the Augustales, a building in Herculaneum. The young man, believed to have been around 20 years old and serving as the college custodian, was discovered in his bed. In 2020, researchers identified fragments of a shiny, glass-like material within his skull, sparking intense debate over whether the substance was truly brain tissue and how it might have been preserved in such an unusual form.
The latest study supports the 2020 findings, confirming the presence of preserved neurons, axons, and brain-specific proteins within the glassy remains. This suggests that the vitrification process was genuine and resulted from the environmental conditions created by Vesuvius’s eruption.
The Role of the Ash Cloud
Herculaneum was struck by both pyroclastic flows—fast-moving currents of volcanic debris, gas, and air traveling close to the ground—and an intensely hot ash cloud that moved at higher altitudes. While the pyroclastic flows in Herculaneum reached temperatures of up to 869 degrees Fahrenheit, the research team found that the brain would have needed to be exposed to temperatures exceeding 950 degrees Fahrenheit, followed by rapid cooling, to undergo vitrification. Since the pyroclastic flows weren’t hot enough to achieve this, the researchers believe that the ash cloud, which was much hotter and short-lived, created the necessary conditions.
Giordano explains that the glass formation required both extreme heat and an almost immediate cooling process. “It’s not the heating process that transforms things into glass,” he says. “The heating process would bake it, would transform it into charcoal, would vaporize it. But it’s not going to make it glass. In order to make a glass, you need a fast cooling.”
The ash cloud, which struck before the pyroclastic flows, may have created the perfect scenario for this rapid heating and cooling cycle.
A Rare and Unique Process
For vitrification to occur, conditions had to be incredibly specific. The skull and spine likely played a protective role, shielding the brain tissue just enough to allow it to cool quickly without being completely destroyed. “The glass that formed as a result of such a unique process attained a perfect state of preservation of the brain and its microstructures,” the researchers write in their study.
The team also found charcoal fragments in Herculaneum that appear to have been subjected to multiple heating events, with the highest temperatures associated with the initial super-hot ash cloud. This further supports their theory about how the glass brain formed.
Scientific Debate
While many experts are intrigued by the findings, some remain skeptical. Alexandra Morton-Hayward, a forensic anthropologist at the University of Oxford, questions whether the glassy material is truly brain tissue, suggesting that soft tissue vitrification is “incredibly unlikely.”
Still, whether or not this discovery represents true vitrification of brain tissue, it remains an astonishing piece of scientific history. The young custodian of the College of the Augustales likely died instantly when the hot ash cloud struck, meaning he never felt the transformation occur. As study co-author Pier Paolo Petrone, a forensic anthropologist from the University of Naples Federico II, notes, “The custodian of the college died instantly from the impact with the hot volcanic ash surge.”
This discovery offers a remarkable glimpse into the devastating power of Vesuvius and the unexpected ways in which it preserved life and death nearly 2,000 years ago.