Remains of rotten fish entrails have helped establish the precise dating of Pompeii's destruction, according to Italian researchers who have analyzed the town's last batch of garum, a pungent, fish-based seasoning.
Frozen in time by the catastrophic eruption that covered Pompeii and nearby towns nearly 2,000 years ago with nine to 20 feet of hot ash and pumice, the desiccated remains were found at the bottom of seven jars.
The find revealed that the last Pompeian garum was made entirely with bogues (known as boops boops), a Mediterranean fish species that abounded in the area in the summer months of July and early August.
"Analysis of their contents basically confirmed that Mount Vesuvius most likely erupted on 24 August 79 A.D., as reported by the Roman historian Pliny the Younger in his account on the eruption," Annamaria Ciarallo, director of Pompeii's Applied Research Laboratory told Discovery News.
The vessels were unearthed several years ago in the house of Aulus Umbricius Scaurus, Pompeii's most famous garum producer.
Garum, made from fermenting fish in saltwater, was basically the ketchup of the ancient Romans. It boasted a much appreciated sweet and sour taste, and was used on almost on every dish, often substituting expensive salt.
Most likelty it was widely available at the numerous open air trattorias, known as thermopolia, where Pompeian "fast food" was served. The sunken jars on the counter contained spiced wine, stews of meat or lentils as well as garum.
Producing garum was relatively simple. A garum maker such as Aulus Umbricius Scaurus would have first placed a layer of fish entrails on a bed of dried, aromatic herbs such as coriander, fennel, celery, mint and oregano.
Then he would have covered the fish entrails under a layer of salt about two fingers high. The layer sequence — herbs, fish and salt — was repeated until the container was filled. The concoction was then left in the sun to macerate for a week or so, and the sauce was mixed daily for about 20 days.
The process produced a smelly liquid — a local delicacy to the Romans.
"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.
The eruption froze the sauce right at the moment when the fish was left to macerate. No batches of finished garum were found, since the liquid evaporated in the heat from the eruption.
"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," Ciarallo said.
Doubts about the date of the eruption emerged a couple of yeas ago when archaeologists discovered a coin which seemed to refer to the 15th imperiatorial acclamation of Titus, believed to have occurred on Sept. 7, 79 A.D.
"Unfortunately, that coin can't be taken as a dating evidence, since it is hardly readable. I myself agree with Ciarallo's dating of the eruption, even though I think that a bit of mystery remains. However, it is not so important whether the eruption occurred in August or in October," Teresa Giove, a coin expert at Naples' Archaeological Museum, told Discovery News.
According to Ciarallo, the date of the eruption on August 24th is also confirmed by biological data.
"All pollen found in Pompeii belong some 350 summer species. I think this is more strong evidence in favor of Pliny's account," Ciarallo said.