Romans loved garum, a salty fish sauce that showed up on tables from Spain to Syria. A new study spells out which fish actually went into it by reading DNA from tiny bones buried in an ancient salting vat.
The team worked at Adro Vello, a Roman era fish processing site on Spain’s northwest coast.
They pulled fragments from the bottom of a vat and extracted ancient DNA, which is genetic material preserved in old remains, to identify the species and peek at past fish populations.
Paula F. Campos, CIIMAR at the University of Porto, is the corresponding author who helped lead the genetic work.
Romans and their sauces
Roman cooks made fish sauces and pastes in large stone vats along the Atlantic and Mediterranean coasts.
Workers salted, crushed, and left small fish under controlled fermentation, which broke down tissues and created a savory liquid that seasoned everything from vegetables to meat.
That process destroyed the usual features scientists use to tell one fish from another.
Bones were shattered, and acids from fermentation damaged the DNA inside them, which makes species identification tough without genetics.
Even so, the Adro Vello bones held enough information to test a clear question. Did Romans really pack these vats with sardines, as some earlier visual identifications hinted.
Reading the recipe
Researchers sampled the residue at the bottom of a single vat and cleaned the tiny vertebrae and scales. They then built DNA libraries and compared overlapping sequences against the reference genome of European sardine.
From those fragments, they assembled the full mitochondrial genome of multiple fish, which is a small circular chromosome inside the cell’s energy factories that helps track maternal lineages. Depth of coverage varied across samples, but it was sufficient to confirm identity.
They also used radiocarbon dating, a technique that estimates age by measuring the decay of carbon isotopes, to anchor the material to the early third century AD. That timeline lines up with the period when this coastal factory was active.
DNA found in the Roman sauce
The sauce makers at Adro Vello were using European sardine. Genetic signatures placed the ancient fish with present day sardines from the central Atlantic Iberian region, which signals continuity across nearly two thousand years.
Population analyses showed less admixture, meaning less mixing between distant sardine groups, than we see in many modern samples.
That result hints at lower connectivity among stocks in Roman times, likely due to different fishing pressure and maritime movement.
These insights do more than satisfy culinary curiosity. They add data points for how human activity and environment shape marine populations over long periods.
How DNA survives fermentation
“In this study, we demonstrate that usable DNA can survive in fermentation environments, such as the brines used by the Romans to make garum,” concluded Dr. Campos.
That is not a trivial point, since acids and microbial enzymes can chop DNA into pieces too small to read.
The team still recovered enough high quality sequences to assemble full mitochondrial genomes and validate species calls with phylogenetic tests.
They also reported calendar dates consistent with the site’s archaeological layers. Those dates, along with clean damage patterns typical of truly ancient molecules, strengthen the case that the DNA is original to the vat and not modern contamination.
Why Roman sauce matters
Foodways reveal trade, labor, and taste. Because garum production plants ringed the coasts, matching species to specific factories helps map supply chains and regional preferences across the empire.
Knowing that Adro Vello used sardines fits finds from other Atlantic facilities. It suggests local fleets targeted schooling fish that could be processed quickly into sauces and pastes for shipment.
Linking ancient and modern sardine genomes also provides a baseline for long term change.
Fisheries managers can compare today’s gene flow and stock structure with a historical snapshot that predates industrial fleets.
From Roman vats to present management
Iberian sardines remain central to coastal economies, and managers in Portugal and Spain use a multi-year plan to set cautious catch limits and seasonal closures.
Those measures follow scientific advice and aim to stabilize biomass through variable recruitment years.
Ancient data will not decide quotas, but it can refine assumptions about how populations connect and change. When models rest on sound baselines, policies stand on firmer ground.
The approach used here can travel well beyond Spain. Similar vats exist across the former Roman world, which means there are many chances to test whether other regions leaned on sardine, anchovy, or mixed catches.
What comes next
The authors plan to sample other sites to see how recipes varied from Africa to the western Mediterranean.
With more genomes in hand, they can test whether regional fleets drew on distinct stocks or tapped a shared pool of fish.
Better reference genomes will only improve the resolution of species calls and population tests. As methods advance, even more degraded residues may yield clear answers.
History often hides in scraps. Here, scraps of bone preserved a record of taste, trade, and the lives of fish that fed an empire.
The study is published in Antiquity.
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