June 14 (UPI) -- When times were good, the dockworkers of Portus, the maritime port of Imperial Rome, enjoyed a surprisingly diversified diet. But new analysis of ancient animal and human remains -- detailed in the journal Antiquity this week -- suggests the diets of the city's working class shifted as Rome fell into decline.
Portus was established in the first century A.D. For four centuries, it served as the Roman's gateway to the Mediterranean and a nexus of maritime trade.
But archaeological analysis suggests the city had taken a defensive posture by the fifth century. Protective walls were built and warehouses, once a place to store imports from North Africa and elsewhere, were used to house the dead.
To better understand how these changes affected the local populace, a research team led by scientists at the universities of Cambridge and Southampton conducted isotopic analysis of animal and human remains found buried in Portus.
"Isotopic analysis works on the principle that you are what you eat -- that your body tissues are made from the food and water you consume," Cambridge bioarchaeologist Tamsin O'Connell told UPI. "We can track chemical signals from the diet into body tissues, to find out about people's diet."
By studying the chemical signals in the bones of ancient Portus residents, scientists can better understand how the region's shifting politics affected people's daily lives.
"The carbon and nitrogen isotopic values of collagen is linked to the types of protein that they consume in their diet -- animal, fish or plant," O'Connell said. "Bones such as ribs form over a period of a few years before death, so they represent a time-integrated signal, not just a recent dietary intake."
Unlike other Roman cities, where scientists have found distinct differences in the diets of the well-heeled and the working class, the latest analysis showed that the dockworkers of Portus ate diversified diets featuring animal proteins, imported wheat, olive oil, fish sauce and wine from North Africa.
The good times didn't last, however.
By the time the Vandals sacked Rome in 455 A.D., the diets of port's dockworkers looked a lot more like the diets of other peasants -- more reliant on plant proteins, portages and stews.
Researchers can't be certain about how exactly political disruption in Rome triggered a simplification of the working-class diet in Portus.
"That's the million quid question. We don't know the causes, but what we have is strong correlation," O'Connell said. "We would now like to look at other sites, to see if we can see a similar shift at the same time."
During the time period, the people of the Mediterranean moved around a fair amount, and it's likely many Portus laborers had to find work elsewhere as the Roman Empire shrank. With its economic reach on the decline, Roman trade shifted eastward.