Dramatic painting shows people cowering from the lava and ash of a volcano in the background

The Eruption of Vesuvius, August 24, AD 79, 1813, Pierre-Henri de Valenciennes. Oil on canvas, 147.5 x 195.5 cm. Toulouse, Musée des Augustins, 7811. Source: Wikimedia Commons. This fanciful depiction of the destruction of Pompeii, foregrounding the death of Pliny the Elder, is titled after the traditional date of the eruption of Mt. Vesuvius.

On August 24, 79, Mount Vesuvius erupted, destroying the ancient Roman cities of Pompeii and Herculaneum. At least, that’s the date inscribed in the history books. As well-publicized recent discoveries have suggested, the volcano may have instead erupted in October.

In this post we’ll introduce you to the evidence for and against an August date, which offers a fascinating case study in the challenges involved in writing the story of the ancient past.

What Do the Texts Say?

The most detailed descriptions of the eruption of Vesuvius appear in two letters from ancient Roman soldier and civil servant Pliny the Younger. Written in late 107 or early 108, they provide vivid eyewitness accounts of the eruption. One letter describes the death of his maternal uncle and adoptive father, Pliny the Elder, as he attempted to investigate the eruption and rescue its victims; the other records the harrowing escape of the younger Pliny and his mother. The first of the two letters provides a date for the event. (You can read recent translations of these letters in the Getty-published book Ashen Sky).

Manuscript page from the Middle Ages with the Latin text of Pliny the Younger's account of the eruption of Vesuvius

Codex Laurentianus Mediceus. Biblioteca Laurentiana, Florence. The traditional date is given in the second and third lines from the bottom (nonum kal. Septembres).

But like most other ancient texts preserved to us, Pliny’s letters only survive through copies made in the Middle Ages. Due both to human error and to changes made deliberately by medieval scribes, today we are often faced with slightly different versions of the same ancient text.

One of the most complete examples of Pliny’s letters is in the ninth-century book known as the Codex Laurentianus Mediceus. This manuscript dates the eruption to the “ninth day before the kalends [first] of September” (in Latin, nonum kal. Septembres)—in other words, August 24. The ancient Romans counted inclusively, numbering both the start and end of a sequence. In this calculation, August 24 + 25+ 26 + 27 + 28 + 29 + 30 + 31 + September 1 = 9 days. This date for the eruption has become canonical.

Other versions of Pliny’s text, however, omit a date or give a different one. A fifteenth-century version in Paris notes the date as nonum kal., (the ninth day before the first), with no month. An edition printed in 1474 has November Calend (the first of November).

Three other versions have Kl. (or Cal.) Novembres, which some scholars believe is a corruption from nonum kal. Novem[bres], i.e., 24 October. In 1797 the Neapolitan bishop and classical scholar Carlo Maria Rosini emended Pliny’s text to read “IX Kal. Decembris,” which would place the eruption a month later still.

What Does Archaeology Tell Us?

Ever since the rediscovery of the buried Vesuvian cities in the eighteenth century, some scholars have argued that the eruption occurred in autumn. Their evidence? The heavy clothing worn by some of the victims, still visible in plaster casts made from the cavities left in the volcanic ash by their bodies. Likewise, braziers were discovered in many houses in the region. Neither would be appropriate for the summer heat of southern Italy.

Other scholars have countered that victims might have donned heavier clothing as they fled the fiery falling ash. And braziers were used for cooking as well as heating, so may well have been used in summer.

One particularly intriguing piece of evidence is a single, badly weathered coin found at Pompeii. It bears an inscription celebrating the emperor Titus’s distinction as imperator, or military victor, for the fifteenth time. We also have two other documents dating to early September 79 mentioning Titus as imperator for the fourteenth time. These must predate the coin. But even this is no smoking gun, because experts still disagree as to exactly when the coin was struck.

What Does Science Reveal?

Scientific research has also contributed to both sides of the debate. Analysis of the remains of ancient fish sauce called garum found in Pompeii seems to support the traditional date in August, because the fish from which it was made were most plentiful in summer.

Archaeobotanical evidence, on the other hand, points to the opposite: pomegranates and walnuts, which would not have been harvested until autumn, were also found.

Mosaic hanging on a gallery wall showing a long, tall jar with a large handle and decorated with Latin lettering

Mosaic from Pompeii depicting an amphora used to store garum, a fermented fish sauce that served as a common condiment in the ancient Mediterranean. Remains of garum found at Pompeii suggest a summer date for Vesuvius’s eruption. Photo: Claus Ableiter, licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported license (CC BY-SA 3.0). Source: Wikimedia Commons

Atmospheric studies, meanwhile, have suggested that the fallout pattern of volcanic ash reflects high-altitude south-easterly winds, which today are prevalent in the region in autumn. Wind patterns may, however, have changed in the almost two thousand years since the eruption.

Just a few months ago, excavators at Pompeii added another piece to the puzzle: they discovered a charcoal graffito dated XVI K Nov, the sixteenth day before the kalends of November—i.e., October 17. Could this seemingly fresh message have been written just days before an eruption on October 24? Or might it have been written the previous year and remained on the wall for ten months before an eruption in August preserved it?

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The Challenges of Writing Ancient History

In our view, the balance of evidence now points to the autumn, perhaps October 24, as the most likely date for Mt. Vesuvius’s eruption. But does the precise date actually matter? Yes—because even small adjustments to dates can change our interpretations of historical events, and thus our writing of history.

In explaining the significance of the date, bioarchaeologist Dr. Kristina Kilgrove notes that the sites buried by Vesuvius are important for understanding demography and disease ecology in the Roman Empire. Since many diseases peak in certain seasons, a difference of two months “is incredibly important to researchers who deal with the analysis of organic remains.” Kilgrove will address this topic at a symposium at the Getty Villa on October 20, 2019, in conjunction with the current exhibition Buried by Vesuvius: Treasures from the Villa dei Papiri.

The various kinds of evidence for the date of the eruption—literary, archaeological, numismatic, archaeobotanical, atmospheric, and epigraphic—and differing interpretations of it challenge how well we know one of the most famous events of antiquity. As we amass new data, ask new questions, and interrogate old assumptions, we gradually build a greater knowledge of and insight to the past.