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Dating the 79AD Eruption of Vesuvius: Is 24th August Really the Date?

The release of the film, Pompeii in 2014, shows that the drama of the destruction of the Roman town by eruption of Vesuvius in 79AD still remains a strong lure to popular culture. While there are always some quibbles with the historical accuracy of films, one aspect of Pompeii that few viewers would have questioned was its summertime setting.


After all, the 24th August is the established eruption date… Or is it?


There is strong evidence to suggest that the catastrophe occurred not in the summer but in the autumn of 79AD.  So what is the evidence surrounding the eruption of Vesuvius? And does it allow us to come up with a definitive date?

Vesuvius and the Remains of Pompeii’s forum, destroyed by the eruption of 79AD. But did it happen in August or October? Image copyright Natasha Sheldon, all rights reserved.

The Problem of the Ancient Texts

The eruption of Vesuvius in 79AD is the earliest datable volcanic eruption on record. Pliny the Younger, in a letter to his friend, Cornelius Tacitus, described it in vivid detail. The date of the eruption in the document has always been quoted as 24th of August. That should be enough to decide the matter. However, there are problems with this.


“The traditional date of 24 August comes from the letter of Pliny the Younger (VI.16). The main manuscripts give ‘nonum kal. Septembres,’ i.e. nine days before the Kalends or first day of September, which on Roman inclusive reckoning is 24 August,” explained Professor Andrew Wallace-Hadrill, Director of the Herculaneum Conservation Project and an expert on Pompeii, during an interview with the author in 2014.


“But another principal manuscript omits the month, and a series of 15th century printed editions, which used manuscripts no longer surviving, give the month as November. Roman dates often were confused in the process of copying manuscripts, so we cannot be sure of the 24 August date, and there is a chance Pliny wrote 24 October. This version is supported by the histories of Cassius Dio, written a century later in Greek, who gives a long description of the eruption (book 66, 21), and dates it ‘kat auto to phthinoporon’ i.e. ‘at the end of autumn.’”


So, the traditional date cannot be relied upon, because of ‘Chinese whispers’ that have occurred between the original document and later copies. However, offers a solution and there is significant evidence to support the October date.


Autumn Fruits and Wine: Botanical Evidence for an Autumn Eruption.

In a 2006 article for Archeo, Grete Stefani, the current site director of Pompeii described the evidence that led her and botanist Michele Borgongino to date the eruption to autumn.

They analyzed the organic wares of shops and warehouses in Pompeii, Herculaneum and Oplontis and found that they consisted of freshly harvested autumn fruits such as pomegranates and walnuts as well as dried dates, prunes and figs which would typically have been fresh during the summer.


Stefani also found evidence that the vindemmia or grape harvest was over and wine production was in full swing. Wine fermenting jars called dolia were found full, sealed and buried at the Villa Regina, at Boscoreale.


Aside from the fact that the harvest would not have occurred until September at the earliest, the wine would have been in production for at least ten days before burial. This coupled with the presence of fresh autumn fruits and summer fruits already preserved suggest an autumnal eruption date.


Tephra Dispersion and the Date of the Eruption

Tephra deposits for the 79 AD eruption back up the botanical evidence. In 2007, Stefani, along with G Rolandi, A Paone and M Di Lascio, began to study the dispersal patterns of deposits of tephra– the rock fragments and ash– emitted during a series of eight other eruptions of Vesuvius. For six of the eruptions, the tephra deposits dispersed in an east-north-east direction. But for the 79 AD eruption and one other, they dispersed in a southeasterly direction.


Wind data collected over a period of 20 years established that from October to June, the prevailing wind conditions matched the northeasterly dispersal patterns of the tephra. But the southeasterly dispersal pattern associated with the 79 AD eruption was more commonly associated with a transitional wind pattern prevalent as the seasons changed from summer to autumn and not the westerly blowing prevailing wind of July and August.


While there can be differences in modern and ancient prevailing winds, this suggests the 79 AD eruption took place during this transitional period- during the early autumn.

Braziers and Winter Clothes

Many of the casts of the bodies of Vesuvius’s victims showed that they were wearing layers of warmer clothing. Some have claimed that people put on heavier clothing to protect them from the eruption. But the presence of used braziers in houses such as the House of Menander suggests that the weather was much colder than we would expect August.

 Numanistics

Coins also add to the picture. A silver denarius minted by the Emperor Titus discovered in the House of the Golden Bracelet has added further fuel to the debate. The coin was found amongst the belongings of fugitives attempting to flee the town: a “defined and documented context” to quote Stefani.


It is the reverse side of the coin that helps date it. Inscribed “TR PVIIII IMP XV COSVII PP”, this describes the honours awarded to Titus: honours that offer evidence of the time frame.


COSVII” refers to Titus’s 7th consulship, which established the coin as 79AD. “TR PVIIII” refers to his 9th period of tribunical power, which was awarded in July of that year. But it is the remaining phrase of the inscription that holds the key. “IMP XV” refers to Titus’s 15th imperial acclamation. In two letters dated the 7th and 8th September, the emperor signs himself using the 14th imperial acclamation.

“This means that the eruption can not have occurred before October 79,” Rosaria Ciardiello, author of “Some Reflections on the House of the Golden Bracelet in Pompeii” told the author.

Garum: Support For an August Eruption

However, Anna Maria Ciarallo, former director of the Pompeii Applied Research Laboratory, believed that garum production in Pompeii proves the August eruption date.


“Pompeii’s last batch of garum was made with bougues, a fish that was cheap and easy to find on the market in those summer months. Still today, people living in this region make a modern version of garum, called ‘colatura di alici’ or anchovy juice, in July when this fish abounds on the markets,” Ciarallo said in an interview with Discovery News.


She continued: “Since bogues abounded in July and early August and ancient Roman recipes recommend leaving the fish to macerate for no longer than a month, we can say that the eruption occurred in late August-early September, a date which is totally compatible with Pliny’s account.”

Pompeii: Can We Date the Eruption?

Ciarallo was not alone in disputing the evidence of Stefani, Borgongino, and others. In an interview with Discovery News, Teresa Giove, a coin expert from Naples Archaeological Museum, dismissed the evidence of the silver denarius, as the coin was “hardly readable.” Ciarallo also countered biological evidence for an autumn eruption with some of her own.


All pollen found in Pompeii belongs to some 350 summer species. I think this is more strong evidence in favor of Pliny’s account,” she told Discovery News.


But most experts now believe that the eruption date was in October. “Today, we don’t think that the date of the eruption was 24th August,” Rosaria Ciardiello told the author.


The reason? Quite simply because the sheer weight of evidence is in favour of October. “In my view,” explained Andrew Wallace Hadrill, “the arguments of Stefano and Borgongino are much stronger than those of Ciarallo.”