The avalanche of gas and rock that spewed from the volcano had been hot enough not only to boil blood and vaporise flesh, but transformed bits of brain tissue into glass, according to a new study published on 22 January in the The New England Journal of Medicine.
"The preservation of ancient brain remains is an extremely rare find", said Dr Pier Paola Petrone, a forensic anthropologist at the University of Naples Federico II and lead author of the study.
Herculaneum sits closer to the base of Vesuvius, about 11 miles (20 kilometres) from the ancient Roman city of Pompeii, destroyed when Vesuvius erupted and covering it in at least 19 feet of ash and volcanic debris.
"This is the first time ever that vitrified human brain remains have been discovered resulting from heat produced by an eruption, " Herculaneum officials said.
They worked this out by testing the shards and analysing the proteins found within them, confirming them as proteins known to be found in the human brain. Though many residents attempted to escape, the researchers' subject made a decision 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. Charred wood discovered within the college indicated that temperatures reached almost 970 degrees Fahrenheit-a clear indication that "extreme radiant heat" was indeed a factor in the man's death. 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.
Scientists say the find is remarkable since brain tissue is rarely preserved due to decomposition, which usually turns remains into a soap.
In October 2018, during one of Petrone's frequent trips to the Herculaneum ruins to study the college and preserve the man's bones, the victim's skull grabbed his attention.
Fragment of glassy material.
"All of this evidence was undeniable evidence that it was the Guardian's brain that was glazed by the high temperature of the ash wave that killed him", said Petrone. He and his team discovered that the victim's brain matter had been vitrified.
Petrone said the finding confirms his theory about how the extreme heat coming from Vesuvius killed people.
The remains were first unearthed during the 1960s at the Collegium Augustalium in Herculaneum, but it wasn't until years later was the body fully examined.
The horrific heat would have "vaporised soft tissues" in the victim's body and burnt all fat in the body.
In nature, the process of vitrification has only been found on vegetable remains, and it's considered the most effective way to preserve human cells and tissues.