When Mount Vesuvius erupted in 79 A.D., hundreds of people in the nearby town of Herculaneum fled to waterfront chambers in hopes of seeking shelter from the catastrophic explosion—a desperate plan that failed to save them from meeting gruesome ends. Among the few who stayed in the town was a roughly 25-year-old man whose ash-covered remains were discovered in a wooden bed during the 1960s.

Now, a new study published in the New England Journal of Medicine suggests a shiny black fragment found within the victim’s skull represents remnants of the man’s brain, which was subjected to such searing heat that it turned into glass.

Located some 11 miles north of Pompeii, Herculaneum was a prosperous seaside town home to between 4,000 and 5,000 people before it was destroyed by Vesuvius’ blast. Though many residents attempted to escape, the researchers’ subject decided to stay behind in the College of the Augustales, “an imperial order devoted to the Roman emperor Augustus,” according to Teo Armus of the Washington Post.

The victim, likely a guard at the college, was killed by Vesuvius’ first pyroclastic surge—clouds of ash, rock and volcanic gas that “move at hurricane velocities and have temperatures of several hundred degrees Celsius,” per the United States Geological Survey.

Pierpaolo Petrone, a forensic anthropologist from the University of Naples Federico II, was examining the man’s remains in October 2018 when he noticed “something was shimmery in the shattered skull,” as he tells Alexandria Sage and Franck Iovene of Agence France-Presse. Petrone immediately suspected the material was brain tissue that had undergone vitrification, a process that occurs when tissue is burned at a high heat and transformed into a glass or glaze.

Human brains are rarely found among archaeological remains. When the organs do surface, they tend to be preserved in the form of a smooth, soap-like substance. As Nicoletta Lanese explains for Live Science, fatty brain tissue reacts with charged particles in the surrounding environment, transforming the organ into soap over time.

Petrone and his colleagues think the extreme conditions caused by Vesuvius’ eruption led something different to happen.

“[E]xtreme radiant heat was able to ignite body fat and vaporize soft tissues; a rapid drop in temperature followed,” the researchers write.

This burst of broiling heat, followed by a cooling of the body, transformed the man’s brain tissue into glass.

Several compelling signs suggested Petrone’s initial hunch was correct. For one, the glassy material only appeared inside the man’s skull; it failed to surface anywhere else on the skeleton, in the surrounding volcanic ash or at other locations within the archaeological site. Charred wood discovered within the college indicated that temperatures reached nearly 970 degrees Fahrenheit—a clear indication that “extreme radiant heat” was indeed a factor in the man’s death.

Testing of the glass samples also revealed fatty acids consistent with those found in human hair, though as the Post points out, animals and vegetables also contain such substances, so the results aren’t conclusive. More compelling was the discovery of several proteins “highly expressed in human brain tissues” within the samples, according to the researchers.

The new report offers further (and rather horrifying) insight into how Vesuvius’ victims died—a subject that continues to confound experts. Yet another new study published in the journal Antiquity suggests the unfortunate ancients suffocated from the volcano’s toxic fumes, their bodies “baking” after they died. This research, in fact, contradicts a 2018 study headed by Patrone, which found that a pyroclastic surge made victims’ blood boil and their skulls explode.

In light of his new findings, Patrone hopes the glassy brain fragments can shed further insight into the identity of the unknown victim. Ancient DNA has previously been used to establish family ties between people who died in Vesuvius’ eruption.

“If we manage to reheat the material, liquefy it,” Patrone tells AFP, “we could maybe find this individual’s DNA.”