In 79 A.D, Mt. Vesuvius erupted, killing thousands of people in the Roman cities of Pompeii and Herculaneum. Currents of hot gas and volcanic matter, ash and gases, as well as subsequent earthquakes caused brutal, widespread devastation. Archaeological evidence even reveals the brain of one young man who died lying in his bed became the only known example of a person’s brain vitrifying—i.e., turning to glass.

Finding brain tissue in an archaeological dig is already fairly rare. When archaeologists do discover ancient brains, they’ve often turned to soap. Researchers believe this victim’s brain turned to glass due to quick changes in temperature as the natural disaster unfolded.

The man whose brain turned to glass died in Herculaneum, an ancient Roman city that was closer to Mt. Vesuvius than Pompeii, and therefore experienced the volcano’s destruction first. He died while lying in a bed at the Collegium Augustalium, a building dedicated to Emperor Augustus. The man was around 20 years old, and may have been a guardian at the Collegium.

Modern archaeologists discovered his remains in the 1960s, but it wasn’t until 2018 that archeologist Pierpaolo Petrone spied the glass in the young man’s skull. In 2020, he and his colleagues published a letter in The New England Journal of Medicine and an article in PLOS One about their preliminary research. They found that the glass in the skeleton contained elements found in the human brain and spinal cord. It appeared that parts of this man’s brain and spinal cord had turned to glass—but how?

In February 2025, they published a new research paper in Scientific Reports outlining a theory for how this could’ve happened. They argue that the brain must have experienced extremely hot temperatures followed by a very quick cooling period.

They suggest this started when a fast, hot ash cloud from the volcano hit the area where the man was sleeping. The extreme heat of the ash cloud, which the researchers estimate was greater than 510 degrees Celsius (950 degrees Fahrenheit), would have killed him. After this brief, extreme exposure to heat, the return to normal temperatures caused his brain to cool down quickly. The volcano’s pyroclastic flow that hit him after this was also hot, but at less than 465 degrees Celsius, it was still cooler than the initial ash cloud.

“Our study demonstrates quantitatively…that the glass transition occurred at 510°C during a fast cooling process,” says Guido Giordano, one of the co-authors of the paper, in an email to HISTORY. “[T]here is no doubt at all that we have discovered a truly vitrified human brain.”

Timothy Thompson, a forensic anthropologist who was not involved with this study, says that he was interested in evidence for how the victim’s brain could have turned to glass. However, he would like to see researchers attempt to replicate the process by trying to turn brain tissue (from a medical donor) into glass through rapid heating and cooling.

“There hasn’t been much research into the effect of volcanoes on human remains,” Thompson says, so there’s still a lot to learn about how people died at Herculaneum and Pompeii.

In 2020, Thompson co-authored an Antiquity paper that addressed how a different group of people in Herculaneum died: those who sought shelter from the volcanic eruption in the stone boathouses on the city’s coast. Though the boathouses helped reduce the level of heat the people were exposed to, it wasn’t enough to save them.

“The remains weren’t burnt in the traditional sense, but they would’ve been baked,” he says.

Archeological studies like these help fill in the gaps of our historical knowledge of the Mt. Vesuvius eruption. Pliny the Younger provided a rare eyewitness account of the disaster in the two letters he wrote about it. But it wasn’t until two thousand years later that anyone learned that the eruption had done something that sounds impossible—turning a human brain to glass.