Almost 2,000 years ago, a young man was lying in his bed near Mount Vesuvius. Suddenly, an extremely hot cloud of ash came down from the erupting volcano.
The heat was so intense that it turned part of his brain to glass.
That is the theory Italian scientists have proposed to explain the strange case of an ancient Roman's brain. They said it is the only human tissue ever known to have naturally turned to glass.
This rare brain could rewrite the story of one of history's most famous natural disasters.
Mount Vesuvius is near the modern-day Italian city of Naples. The volcano erupted in the year 79 AD, covering the cities of Pompeii and Herculaneum with a fast-moving layer of rock and ash called a pyroclastic flow.
Thousands of bodies have been discovered in the two places. They are frozen in time, showing people today the daily life of ancient Rome.
In the 1960s, the burnt remains of a man about 20 years old were found on a wooden bed in a building in Herculaneum used for the worship of the Roman Emperor Augustus.
Italian anthropologist Pier Paolo Petrone, a co-author of a new study, noticed something strange in 2018. What was left of the man's brain had been changed into pieces of shiny black glass.
Surprising finding
Guido Giordano is the lead writer of the study published in Scientific Reports in February. He told the French News Agency (AFP) that these pieces are up to a centimeter wide.
When the scientists studied the glass using an electron microscope, they discovered an "amazing, truly unexpected thing," he said.
This is even more unlikely to happen to human tissues because they are mostly made out of water.
The Roman's brain being preserved in glass is the "only such occurrence on Earth" ever documented for human or animal tissue, the study said.
The scientists said that the brain must have been exposed to temperatures above 510 degrees Celsius.
That is hotter than the pyroclastic flow that buried the city. Then the brain needed to rapidly cool down. All this had to happen before the flow arrived.
The scientists think this only could have happened if the ash cloud from Vesuvius sent out a very hot blast before the pyroclastic flow arrived.
This theory is supported by evidence of a thin layer of ash that settled in the city shortly before it was covered by thick layers of rock and ash.
This would mean the people of Herculaneum were actually killed by the ash cloud -- not the pyroclastic flow as had long been thought.
'Poorly studied' threat
Giordano hoped the research would bring more attention to the threat of these hot ash clouds. They remain "very poorly studied" because they leave little evidence behind.
French volcanologists Katia and Maurice Krafft were the subjects of the 2022 documentary film Fire of Love. They were killed by such an ash cloud, Giordano said.
And some of the 215 people killed during the 2018 eruption of Guatemala's Fuego volcano were also victims of an ash cloud, he added.
"There is a window of survivability" for these hot blasts, he said, adding that building houses which can resist high heat near volcanoes could help.
But why did the man with the glass brain alone suffer this fate?
The other citizens of Herculaneum had some time to run away from the eruption. All the other bodies discovered there were clearly trying to flee.
But the man, who is thought to have been the guardian of the Collegium building, stayed in bed in the middle of town, so he was the first hit.
Giordano said that we will likely never know the whole truth of what happened that day.
crystallization - n. the process in which cooling minerals form regular geometrical shapes
meteorite - n. a piece of rock or metal that has fallen to the ground from outer space