Modern volcanology classifies the 79 CE event as a Plinian eruption, a Volcanic Explosivity Index 5. It ejected roughly 1.5 cubic kilometers of tephra and drove an eruption column to a height of about 33 kilometers, well up into the stratosphere.

The reconstruction worked out by Haraldur Sigurdsson and Steven Carey, and by Giuseppe Mastrolorenzo and colleagues, splits the eruption in two. Phase one, lasting about eighteen hours, was a sustained Plinian column that rained white pumice down on Pompeii to a depth of around 2.6 meters, followed by grey pumice. Phase two began when that column collapsed, generating six pyroclastic density currents, the surges and flows of superheated gas and rock that did the real killing.

Herculaneum sat closer to the vent, about 7 kilometers away against Pompeii's 10, and it died first. The opening pyroclastic surge overwhelmed the town at around one in the morning, while Pompeii was still being buried under falling pumice.

At Pompeii the fourth of the six surges arrived at about half past seven the following morning. It killed the inhabitants who had stayed, by thermal shock, at temperatures estimated between 250 and 300 degrees Celsius.

When it was over, the burial was deep and fast. Pompeii lay under 4 to 6 meters of pumice and ash. Herculaneum, swamped by successive flows, lay under as much as 20 meters of pyroclastic material. That depth is a large part of why the two towns survived so intact.

Vesuvius had given a sign seventeen years earlier. Seneca records a severe earthquake that damaged Pompeii on February 5 in the year 62 (Naturales Quaestiones VI.1), and the archaeology backs him up: many of the town's buildings were still under repair when the eruption came in 79. Volcanologists have suggested that earthquake was driven by magma moving beneath the mountain in the preceding decades, though the exact link between the tremor and the eruption that followed remains debated.

Gaius Plinius Caecilius Secundus, whom we call Pliny the Younger, was about 17 when Vesuvius erupted. Around 106 to 107 CE he wrote two letters to the historian Tacitus describing what he had seen, Epistulae 6.16 and 6.20. They are the only surviving eyewitness account of the disaster, from anyone.

Letter 6.16 is about his uncle. Pliny the Elder, a naval commander and famous naturalist, sailed from Misenum straight toward the eruption to rescue friends stranded at Stabiae. He never came back. He died there, most likely of cardiac arrest or asphyxiation from the volcanic gases.

Letter 6.20 is Pliny's own story from Misenum: the ground heaving with earthquakes, pumice falling, and a darkness he described as unlike a moonless night, more like a room with the lamp extinguished. It is from these two letters that volcanology takes the name for this kind of eruption. A Plinian eruption is named for the boy who watched this one.

Systematic excavation began at Herculaneum under Karl Weber in 1748, and at Pompeii under Rocque Joaquin de Alcubierre from the same year. The single most important technique came later, from Giuseppe Fiorelli, who took over at Pompeii in 1860. In 1863 he developed the plaster-casting method: where a buried body had decayed inside the hardened ash, it left a cavity in the exact shape of the person, and pouring liquid plaster into that void recovers the form of a Pompeiian in the last moment of life.

About two-thirds of Pompeii's 66-hectare site has now been excavated, uncovering more than 1,500 buildings. Among them are the Forum, an amphitheater that seated roughly 20,000, public baths, brothels, and private houses whose frescoes, mosaics, and scratched graffiti survived two thousand years underground.

That excavation is also the site's biggest problem. Andrew Wallace-Hadrill and other conservation specialists have argued that exposing buildings faster than they can be conserved has let structures and frescoes that survived two thousand years underground decay in the open air. The crisis was serious enough that in 2012 the Great Pompeii Project, the Grande Progetto Pompei, was created with about 105 million euros in European Union funding to stabilize what has already been dug.

In 1982, excavations led by Giuseppe Maggi opened the vaulted stone chambers, the fornici, along what had been Herculaneum's waterfront. Inside were the skeletal remains of about 300 people. They had gathered there at the edge of the sea, sheltering in the boat houses and waiting for a rescue by water that never reached them.

What killed them, and how fast, is written into their bones. Study of the boat-chamber victims by Sara Bisel, and later by Pier Paolo Petrone and colleagues, found the marks of instantaneous death. A 2018 paper in PLOS ONE reported black staining on the inner surface of some skulls, consistent with brain tissue that had boiled. A follow-up in 2020, in the New England Journal of Medicine, described something rarer still: vitrified brain material, the first archaeological evidence of a human brain preserved by rapid thermal vitrification, at temperatures estimated between 400 and 500 degrees Celsius. These were people who died in the instant the heat reached them, faster than the body can register.

The Villa of the Papyri, dug by Karl Weber in the 1750s through narrow underground tunnels, gave up around 1,800 papyrus scrolls. The heat had carbonized them, charring them into fragile black cylinders rather than burning them away, which is the only reason any of them still exist. Most hold works by the Epicurean philosopher Philodemus of Gadara. It is the sole surviving library of antiquity.

For centuries the scrolls were unreadable, too fragile to unroll without destroying them. That changed in 2023. The Vesuvius Challenge, built on AI-driven X-ray micro-CT scanning and machine learning developed by Brent Seales at the University of Kentucky, read passages from unopened scrolls for the first time, pulling philosophical text on pleasure and the senses out of a cylinder no one has ever physically opened.

And the villa may not be empty yet. Parts of its library are thought to lie in deeper chambers that have never been excavated. Scholars allow themselves to hope the unrecovered sections could hold lost works of Greek and Latin literature, plays by Sophocles or Euripides, treatises by Aristotle, missing books of Livy, though this is speculation rather than expectation. Political, structural, and conservation concerns have kept anyone from tunneling deeper since the 18th century.

Vesuvius belongs to the same Campanian volcanic province as the Campi Flegrei caldera, the restless ground about 15 kilometers west of Naples. Campi Flegrei's own Campanian Ignimbrite super-eruption, around 39,280 years ago, was a Volcanic Explosivity Index 7 event that threw out an estimated 250 to 300 cubic kilometers of tephra, something like 170 to 200 times what Vesuvius ejected in 79 CE, and the largest volcanic event in the Mediterranean region in the past 200,000 years.

And Pompeii was not the first Mediterranean city buried by fire. Akrotiri, on the island of Thera, modern Santorini, is often called the Pompeii of the Bronze Age. It was entombed by its own volcano roughly 1,600 years earlier, around 1600 BCE, and its preservation is as good as Pompeii's, sometimes better. But there is one haunting difference. Where Pompeii has yielded around 1,150 bodies, Akrotiri has produced none. Everyone there seems to have gotten out in time.

Start with the date, because it is no longer settled. During 2018 excavations in Regio V at Pompeii, archaeologists found a charcoal graffito reading XVI K NOV, the 16th day before the Kalends of November, which is October 17. Set alongside other autumn signs at the site, pomegranates, wine still in the pressing, warm clothing on some of the victims, it points to an eruption in late October of 79 CE rather than the traditional August 24.

The August date was never as solid as it looked. It comes from a medieval manuscript tradition of Pliny's letters, where the phrase Nonum Kal. Septembres, the ninth day before the Kalends of September, August 24, may be a copyist's slip for Nonum Kal. Novembres, October 24. A single miscopied word could account for the whole discrepancy.

But the October case is not closed either. Mary Beard and others have pointed out that a single charcoal graffito proves less than it seems: charcoal writing is casual and impermanent, and that note could have been scrawled days or even weeks before the eruption sealed it. The honest position, and the one the evidence currently supports, is that we do not know for certain in which month Pompeii died.

A second, quieter question is whether the eruption also sent water. Researchers have proposed that pyroclastic flows pouring into the Bay of Naples could have generated localized tsunamis along the coast. It is plausible on the physics, but no clear geological or archaeological deposit from such a wave in 79 CE has ever been conclusively identified. For now it stays a possibility, not a finding.

And then there is the oldest story ever told about Pompeii's end, that it was punishment. Some early Christian writers read the eruption as divine retribution for the town's supposed depravity, pointing to its erotic frescoes and its brothels. That reading does not survive contact with the archaeology. The erotic art at Pompeii is ordinary Roman decorative convention, found in respectable homes across the empire, and Pompeii itself was a typical prosperous Roman town, no more debauched than its neighbors. The eruption was a geological event, not a verdict.