In A.D. 79, Mount Vesuvius exploded in one of the most violent volcanic eruptions in history. Reconstructions of the event vary, but the overall details remain the same: Vesuvius erupted around 1 p.m. local time, spewing a giant column of ash and pumice. Many people escaped during this time.

Those that remained must have witnessed one of the most horrifying scenes ever known to mankind. Hours later, pyroclastic flows began. The lava was fast-moving and hotand it destroyed everything in its path. Several Roman settlements (and the people in them) were destroyed during the event. One of the most famous, perhaps, is the city of Pompeii.

For centuries, people around the world have been fascinated by what remains of the civilization. Hundreds of corpses have been discovered, perfectly preserved, in shockingly contorted poses. Many of them died before the lava flows even started, falling victim to collapsing houses or plunging stone. For many years, it had been assumed that the others died of suffocation, unable to breathe in the onslaught of toxic gasses. But now researches are rethinking that.

Could They Have Suffocated?

The old theories do hold plenty of merit. Casts of the victims show that many of them appear to be covering their nose and mouthsuggesting that, perhaps, they were trying to shield themselves from the contents of the air around them.

If they did succumb to asphyxiation, it would have been truly horrible: Burning hot gasses such as carbon dioxide, hydrogen sulfide, and sulfur dioxide would have seared their airways as they were inhaled. Mixed with the fine ash, they would have formed a sort of cement in the victims’ lungs, making respiration impossible.

For many researchers, the victims’ “pugilistic poses” are evidence of this gruesome death. The victims appear to be trying to defend themselves, but the agony on their faces clearly shows that they knew they were doomed.

Death By Thermal Shock

A growing number of researchers suggest that it was actually the extremely high heat the killed many of the victims. While Pompeii and the surrounding cities were hit by a blast of gasses and debris, it was likely the temperatures killed them in what was a more disturbing (but ultimately quicker) sort of death.

According to Dr. Peter Baxter of Cambridge University, “The direct heat of the surge would be combined with the radiant heat of the ash particles in the cloud to cause rapid fourth-degree burns, i.e., burns extending below the skin layer and into the muscles/deep tissues, with rapid overheating of the blood returning to the heart causing cardiac arrest and/or the brain causing respiratory arrest.”

Luckily, it all would have happened very fast.

Can It Happen Again?

Many of the victims discovered in Herculaneum were frozen in semi-contorted poses. This suggests that the heat could have destroyed some of their muscle faster than it could contract. And, in fact, research suggests that a single blast of heat of roughly 450 – 500 degrees Fahrenheit killed most people.

But could it happen again? It is still an active volcano, so likely yes–and these days more than 3 million people are at risk.