Even if you’re someone who knows very little about volcanoes, chances are good you’ve heard of Mount Vesuvius. It last erupted in 1944, but that was nothing like the first time it blew its top. The destruction was widespread and cataclysmic, but there remains an element of mystery to the story: When did it happen?

Bathed in ash

Mount Vesuvius is located on the southwestern coast of Italy, just south of the city of Naples. Back in the first century AD, the volcano was surrounded by flourishing cities, the most notable of which were Pompeii, to the south, and Herculaneum, immediately to the west. When Vesuvius erupted, it coughed tons of ash and rock into the sky and released hot gases that blanketed the surrounding countryside. When it wasn’t belching out pyroclastic solids, Vesuvius was oozing lava, alternating between the two states a dozen times throughout the eruption.

Pompeii was buried in the hot ashes and rocks that fell from the primary or Plinian eruptions. Herculaneum, which was slightly upwind of the volcano, faced a far gnarlier demise in the superheated gases that rolled down the mountain’s sides, incinerating everything in its path. Several other cities were destroyed, but Pompeii and Herculaneum are by far the most well-recognized.

Context clues

Traditionally, the date of Vesuvius’ eruption is said to be August 24. Since the 1800s, historians have been debating the accuracy of that date. Instead, they’ve argued that the catastrophe happened sometime in October of that year. With few surviving written records from the time, geologists have had to use other clues to piece together the truth. Based on that information, the record books may soon be changing. A series of coins, inscriptions, buried goods, and meteorological evidence suggests that the eruption took place sometime in mid-October rather than mid-August as has been claimed for so long. While the new information doesn’t alter the facts of what happened, it might help historians rearrange their timelines and shed light on simultaneous events.