When Mount Vesuvius unleashed its fury in A.D. 79, Herculaneum was just one of several towns smothered by ash and savaged by superheated volcanic avalanches. But three centuries after excavations began, experts are still unsure as to what precisely killed the victims of this once bustling metropolis.

Along with collapsing buildings, flying debris, and stampedes of fleeing residents, various studies have blamed the inhalation of ash and volcanic gases, a sudden heat shock, and even the vaporization of people’s soft tissues.

Now, two studies add a couple twists to the tale.

One concludes that those taking cover in the town’s boathouses were not really burned or vaporized, but instead baked as if inside a stone oven. The second has found a victim in a different portion of the city whose brain appears to have melted before being frozen into glass, as if afflicted by sorcery.

Even if these two tales of biological transmogrification are verified by future research, it does not mean we finally know how these people died. All that can be said is that this may be what happened around the time of their death. (Also find out about horses found preserved at Pompeii that appear to have been harnessed to help people flee the disaster.)

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With so much clear-cut evidence lost to time, “we'll probably never be able to know the ultimate truth” of how they died, says Elżbieta Jaskulska, an osteoarcheologist at the University of Warsaw, who was not involved with either study. But endeavoring to solve this puzzle is worthwhile, and not just because it fills in missing chapters of an iconic story.

“Volcanic disasters don’t just happen in the past,” says Janine Krippner of the Smithsonian Institution’s Global Volcanism Program, who was not involved with the work.

Plenty of volcanoes worldwide are capable of producing similar outbursts, which means history will keep repeating itself. Understanding how those volcanic avalanches have harmed people in the past could allow first responders to better equip themselves to treat those who, although injured, manage to survive a volcano’s future wrath.

Mind-blowing … if true?

Back on that summer’s day in A.D. 79, volcanic avalanches of hot ash and gas, moving at around 50 miles an hour, were unquestionably Vesuvius’ most mortifying feature. These are often called pyroclastic flows, but the gassier versions that swamped Herculaneum are named pyroclastic surges.

Many of the victims swept up by the eruption were long thought to have died by asphyxiating on ashes and toxic gases. A series of studies in the last two decades co-authored by Pier Paolo Petrone, a paleobiologist at the Federico II University Hospital in Naples, suggested that the surge temperatures were so high that many people’s internal organs suddenly shut down, a death through extreme thermal shock.

In 2018, Petrone and his colleagues reported reddish, iron-rich compounds on the often-cracked bones of several Herculaneum victims. This spatter, they said, came from the destruction of red blood cells as those scorching surges vaporized the victims’ soft tissues—like their muscles, tendons, nerves, and fat. Boiling fluids in the brain would have also created pressure and caused their skulls to explode. These claims were met with skepticism by some experts, who noted that bodies being cremated at far higher temperatures do not experience vaporization.

This debate remains unsettled—but a new study by Petrone and company, published this week in the New England Journal of Medicine, will only add more fuel to the fire.

Soap and glass

Cerebral tissues in archaeological discoveries are extremely rare. Even when found, they are often unpreserved, having turned into a soapy mixture of compounds like glycerol and fatty acids. Petrone decided to take a closer look at one particular victim, found in the 1960s inside the Collegium Augustalium, a building dedicated to the cult of Emperor Augustus, who ruled Rome from 63 B.C. to A.D. 14.

Unexpectedly, a glassy substance was found inside the cracked skull , which was surprising because the eruption itself produced no glassy volcanic material. The skull’s glass contained proteins and fatty acids common in the brain, as well as fatty acids typically found in the oily secretions of human hair. No plant or animal sources of these substances were located nearby.

The glassy shards, Petrone explains, are likely the remains of the victim’s brain—and the first example of its kind ever found in any ancient or modern context.

This tissue-turned-glass had to have been created by vitrification, a process wherein a material heats until it liquifies and then very rapidly cools into glass rather than an ordinary solid. Charred wood nearby suggests that the temperatures in the building potentially reached 968 degrees Fahrenheit. This was seemingly hot enough to ignite body fat, vaporize soft tissues, and melt brain tissue. The brain matter was then suddenly quenched, but Petrone says what permitted that to happen currently remains a mystery.

“It’s amazing and horrifying at the same time to think that such intense heat can turn your brain into glass,” says Miguel Vilar, a biological anthropologist at the National Geographic Society, who was not involved with the work.

But the vitrification process here is not yet fully fleshed out, and because it isn’t clear why the fate of this victim’s brain is (at present) unique among the volcano’s victims, it cannot be said for sure that this is truly vitrified brain matter.

Baked not burned

The other new paper, appearing this week in the journal Antiquity, examined remains that point to a different end for people who died along Herculaneum’s waterfront. Men gathered on the beach, perhaps trying to arrange a seaward evacuation, while women and children mostly took cover in stone boat chambers named fornici. Everyone perished, and to date, 340 bodies have been excavated from the area.

The victims’ bones were long seen as nothing more than annihilated remnants. But in the past decade, new scientific techniques have been able to analyze burned human fragments to provide windows into the time around these people’s deaths.

“You can actually tell a lot about someone’s life from their cremated remains,” says Tim Thompson, an applied biological anthropologist at Teesside University in England. So, he and his colleagues thought, why not apply these techniques to Vesuvius victims?

The team examined rib bones from 152 individuals in six of the 12 fornici. They looked at the quality of collagen, a key protein that is fairly robust over long timescales but that can nevertheless deteriorate in the presence of, among other things, high temperatures.

View Images A group studies body casts in the House of Cryptoporticus while touring the ruins of Pompeii. In addition to this city near modern-day Naples, the port town of Herculaneum and many other sites near Mount Vesuvius were buried by its pyroclastic flows and surges in A.D. 79. Photograph by David Hiser, Nat Geo Image Collection

Of those 152 people, only 12 showed highly deteriorated collagen. Most of those 12 samples came from children, whose less mineralized skeleton would leave their collagen more vulnerable to breaking down over time. There is also an experimentally proven correlation between the degree to which a bone has been crystallized and its exposure to high temperatures. The team found that these victims’ bones had low levels of crystallization.

Both findings indicate—convincingly, says Jaskulska—that the fornici victims were not exposed to extremely high temperatures from the pyroclastic surges at the moment of or shortly after their deaths.

Various studies looking at the altered magnetic properties of materials, the damage to plasters, wood, and mortars, and so on have estimated a range of temperatures for the eruption’s pyroclastic surges. These range from highs of 1,472 degrees Fahrenheit down to lows of 464 degrees Fahrenheit.

The new study suggests the lower end of the range is more plausible. Even at those cooler temperatures, the victims’ bones should have experienced more damage. The absence of this harm means the cadavers had additional protection from the surges.

The heat damage was likely reduced by the intact fornici walls, given that the people were found in close proximity. Swelling outer tissues and internal water pooling around long bones also meant the skeletons were baked rather than burned.

Crucially, the victims were not being ignited on a pyre; instead, the surges heated the air around them, which is less effective at destroying human tissue than actual fire.

Death in darkness

What didn’t transpire, Thompson says, was any soft tissue vaporization. Even at temperatures exceeding 1,200 degrees Fahrenheit in controlled cremation studies, it takes at least 40 minutes for human tissue to be fully destroyed. Pyroclastic surges cannot come close to replicating these conditions.

“As an idea, it just doesn’t hold weight,” Thompson says.

Petrone agrees that huddled masses would have more protection from heat damage. But he disagrees that temperatures were low inside the fornici, pointing to the glassy-brained victim inside the Collegium, whose skeleton was charred and fractured, and whose skull seemingly exploded due to high surge temperatures.

Scientific schisms aside, no one doubts that the final moments of these people’s lives would have been nightmarish, Thompson says. They died trembling in darkness, through extreme heat exposure or suffocation. Pliny the Younger, a Roman lawyer and author who observed the eruption from a distance, recalled in a letter that some people were so frightened by the event that they actually prayed for death. Many begged for the help of the gods, he wrote, but even more imagined that there were no gods left, and that the last eternal night had fallen on the world.