Pliny the Younger was just a teenager when he witnessed the total destruction of Pompeii by the devastating eruption of Mt. Vesuvius in A.D. 79. His uncle died in the historic eruption, and Pliny’s descriptions of the event in letters to the Roman historian Tacitus are the only surviving eyewitness accounts of one of the largest and deadliest volcanic eruptions of the ancient world.

Most of the estimated 2,000 deaths at Pompeii occurred on the second day of the eruption, when the top of Vesuvius collapsed and an avalanche of raging-hot volcanic material tore through the city. This fast-moving wall of hot rock and ash, known as pyroclastic flow, killed with both heat and sheer force. The famous plaster casts of Pompeii’s victims are so lifelike because they were buried and killed almost instantly.

But it’s also likely that some of the victims at Pompeii weren’t killed by the volcano itself. According to Pliny, the eruption of Vesuvius was also accompanied by earthquakes—and now evidence confirms that powerful earthquakes did, in fact, rattle Pompeii following the eruption.

Pliny was 18 miles away from Vesuvius and he describes violent earthquakes that struck overnight and again at dawn of the second day. “[The] earthquakes… that night became so intense that everything seemed not only to be shaken but overturning,” wrote Pliny. “It was the first hour of the day, but the light was still faint and weak.…the chariots we had ordered to be brought out, though on a level ground, were shaken back and forth and did not remain steady in their places even wedged with stones.”

Until now, there’s been no clear archeological evidence at Pompeii of deaths caused by Vesuvian earthquakes alone, because the devastation of the pyroclastic flow made it nearly impossible to distinguish between seismological and volcanic damage.

But a team of scientists in Italy found compelling evidence at Pompeii of deaths from an earthquake-induced building collapse, not heat or asphyxiation. The discovery not only confirms Pliny’s 2,000-year-old account, but may rewrite the story of why so many people perished at Pompeii.

Until this discovery, published in Frontiers in Earth Science, the conventional archeological account of the deadly Vesuvius eruption was that it occurred in two distinct phases.

Around 1 p.m. on the first day, Vesuvius erupted with a massive explosion, ejecting a column of volcanic material nearly 20 miles into the sky. (This particular type of eruption is called a “Plinian” eruption, named after Pliny the Younger’s detailed description of the volcanic event.) During the first phase of the eruption, material rained down on Pompeii in the form of pumice lapilli, tiny lightweight stones formed from bits of expelled lava rapidly cooling in the air.

“Pumice lapilli isn’t very hot, but it rained down for 18 hours straight and accumulated to depths of up to three meters (nine feet),” says Domenico Sparice, an Italian volcanologist and co-author of the Frontiers paper. “The weight of the pumice lapilli deposits caused roofs in Pompeii to collapse and many people died as a consequence during that first phase.”

For those who survived the long night, there was a brief respite shortly before dawn on the second day. For about half an hour, the storm of pumice stones stopped. Some of the survivors of the first phase may have crawled out their second-floor windows onto streets covered in loose rock and ash, and attempted to flee the city. Others hunkered down in their homes waiting to be rescued.

“They may have thought that the worst was over,” says Sparice, “but it was not.”

With another earth-shaking eruption, the second phase began. This time, it wasn’t a shower of lightweight rocks, but a searing wall of death moving at the speed of a freight train. Whether in the streets or in their homes, the unwitting citizens of Pompeii had no chance of surviving the pyroclastic flow.

“It’s like a hot avalanche of volcanic material,” says Sparice. “It’s a mixture of gas and volcanic particles moving at a high speed and high temperature on the ground.”

In as quickly as 15 minutes, thousands of Pompeii’s residents died from a mixture of heat, asphyxiation from ash inhalation, and the brute force of the pyroclastic avalanche, which toppled walls and collapsed entire buildings.

Sparice and his fellow scientists don’t dispute the claim that the majority of Pompeii’s victims died during the pyroclastic flow phase. But now they have evidence pointing to an important third phase of destruction. Sandwiched between the shower of pumice stones and the pyroclastic flow was a powerful earthquake registering as high as 5.8 on the Richter scale.

Pliny described powerful earthquakes striking overnight and in the early hours of the second day, but there was never any clear evidence from the archaeological record that these quakes constituted a third, independent phase of destruction at Pompeii. That’s exactly what Sparice and his team believe they’ve found.

The evidence comes in the form of two sets of human remains discovered in the ruins of Pompeii. The two skeletons were found under a collapsed wall of a home. They appear to be two men in their 50s who suffered multiple severe compression fractures to the rib cage, pelvis, limbs and skull.

According to anthropologists, the men’s injuries aren’t consistent with death from asphyxiation or heat, but from blunt force trauma. In fact, Sparice says, the type of compression trauma that killed both men is almost identical to that of victims found in the wreckage of modern earthquakes.

In most cases where buildings collapsed in Pompeii, they were knocked down by the crushing force of the pyroclastic flow, but the home where the two men died strays from the expected pattern of destruction.

“When a pyroclastic current hits a wall, it completely destroys the wall, or results in overturning or toppling,” says Sparice. “Here, this was not the case.”

By reconstructing the scene, it appears that the heavy wall that killed the men was first horizontally displaced by seismic activity—violent, side-to-side shaking—and then slipped down on top of the victims, crushing them. Another clue is that the collapsed wall was covered with a layer of pumice lapilli. That means that the wall fell while the lightweight rocks were still raining down.

The proposed timing of the wall collapse aligns perfectly with Pliny’s description of the worst shaking around dawn of the second day. The earthquake hit at the tail end of the first eruption phase, when light debris was still falling. That was at least 30 minutes before the arrival of the pyroclastic flow, meaning that these two deaths were caused by an earthquake, not the volcano.

“This is the first time that we found a building collapse that we can confidently associate with earthquakes,” says Sparice, whose team is already looking for more clues of earthquake damage in the historic ruins of Pompeii.

The discovery has led to a new hypothesis about the fate of the 2,000 victims in Pompeii. A number of people likely survived the initial “Plinian” phase, when Vesuvius blew its top and rained down debris on the city below. But their chances of escaping the city before the arrival of the deadly pyroclastic flow were all but erased by a major earthquake that likely toppled untold numbers of buildings across Pompeii.