The Antonine Plague: the killer disease that devastated the Roman empire

Exposing the vulnerabilities of the Roman state, the Antonine Plague struck across an approximate 15-year period, from AD 165 to 180. Outbreaks decimated the Roman population, economy, and military, marking the disease as one of the most significant pandemics in ancient history. Some historians have it that the plague may have even sowed the seeds of the empire’s decline and eventual collapse.

What was this disease that wreaked so much havoc, and where did it come from? Here, with expertise from Professor Colin Elliott, we track the plague’s path of destruction through the Roman world…

What was the Antonine Plague?

The Antonine Plague was a deadly epidemic that devastated the Roman empire. It takes its name from Antoninus, the imperial family name of Marcus Aurelius and Lucius Verus, who ruled as co-emperors at the time of the first outbreak.

Although referred to as a plague, this was not bubonic plague (a disease better known as the Black Death, which ravaged medieval Europe a millennium later). In fact, the identity of the disease remains unknown, despite numerous theories and speculations.

“We don’t know what disease it was,” says Professor Colin Elliott, author of Pox Romana: The Plague that Shook the Roman World (Princeton University Press, 2024).

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Smallpox and measles are common culprits blamed for the Antonine Plague, but without conclusive evidence. “We don't have the DNA evidence to confirm a smallpox diagnosis or a smallpox-like disease diagnosis,” Elliott explains on an episode of the HistoryExtra podcast. “In fact, if anything, the genetic evidence suggests that it was not.”

Whatever specific disease it was, stresses Elliott, “it was contagious and obviously very deadly”.

A timeline of the Antonine Plague: when did it start?

The Antonine Plague first emerged around AD 165 within the ranks of the Roman army, before spreading across the empire. The epidemic reached its peak by AD 166–168 and was followed by further waves over the next decade, eventually receding around AD 180.

The initial outbreak occurred during the military campaign against the Parthians, in modern-day southwestern Asia.

“Emperor Lucius Verus took tens of thousands of soldiers and marched them down the Euphrates [river] into Persian territory,” says Elliott. “We're told in several literary accounts that they encounter some kind of new diseases.”

After securing victory in the Roman-Parthian War, Lucius Verus’s soldiers returned home, bringing the new disease with them.

By AD 166, the epidemic had reached the heart of the empire, Rome itself. “The soldiers that were in Parthia came back to their European bases and some were selected to participate in a triumphal parade,” says Elliott. “There would have been thousands of troops invited into the city of Rome.”

They marched through the streets, taking a circuitous route that hit all the major sites and temples, and were watched by large crowds all the way. As Elliott points out, “Rome's population at this time is probably over a million people; if 10 per cent showed up to watch this parade, that's 100,000 people.”

That, Elliott adds, is what we would in modern parlance call a “super-spreader event”. Following the triumphal parade, the outbreak worsened immediately.

How far did the Antonine Plague spread?

Facilitated by the empire's extensive trade networks and movement of troops, the Antonine Plague spread rapidly. It affected the entire Mediterranean Basin, reaching Egypt, Greece and Gaul.

While the most severe impact was felt in the early years between AD 166–168, accounts indicate that waves continued to flare up sporadically until AD 180.

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By the time that Emperor Marcus Aurelius died in AD 180 (his co-emperor, Lucius Verus had perished in AD 169, perhaps from the Antonine Plague) the outbreaks had gradually subsided.

The end of the disease’s prevalence wasn’t marked by a specific event, but rather a slow reduction in mortality and infection rates. As Elliott explains, the Antonine Plague “vanished because enough immunity built within the population so that the disease could no longer latch on to large populations and have these epidemic bursts”.

What were the symptoms of the Antonine Plague?

The symptoms of the Antonine Plague included: high fever, vomiting, inflammation of the throat, severe skin rashes that scabbed and scarred or formed pustules, and ulcerations inside the body. Diarrhoea was also common: bowel movements would be red or even black, suggesting gastrointestinal bleeding.

This information primarily came from the accounts of the physician Galen, who worked practiced medicine during the epidemic. As such, it is sometimes referred to as the Plague of Galen.

The symptoms lasted two weeks, but not everyone who contracted the disease would die. The fatality rate has been estimated to as high as 35 per cent.

What was the Antonine Plague’s death toll?

Estimates suggest that the death toll from the Antonine Plague is likely to be between 5 and 10 million people, accounting for roughly a fifth to a quarter of the population of the Roman empire. However, this remains difficult to precisely quantify.

Soldiers of the Roman legion were particularly hard-hit, due to their movements from region to region and living in such close proximity to one another. Some reports indicate that entire units were rocked by casualties, weakening the military’s ability to defend the empire.

Cassius Dio, a Roman historian writing after the epidemic had receded, claimed that 2,000 people were dying every day.

What was the impact of the Antonine Plague on the Roman empire?

The Antonine Plague impacted every aspect of Roman empire, destabilising the military and economy.

Moving from region to region and living in such close proximity to one another, soldiers of the Roman legions were particularly hard-hit, with reports indicating that entire units were rocked by casualties, weakening the military’s ability to defend the empire.

When the disease first appeared, the army was engaged in multiple campaigns; ironically, maintaining Pax Romana was achieved through war, more importantly victory. As soldiers perished from the disease, however, the army could no longer defend the empire or suppress rebellions as effectively. The result was a general decline in the invincible aura of the Roman army.

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The Antonine Plague did not itself destroy the Pax Romana, as Elliott explains, but certainly had a noticeable impact. “It accelerated soldier deaths, which prolonged the wars, which then created an unstable situation on the borders. This contributes, in a way, to the fall of the Roman empire.”

On an economic level, the Antonine Plague was equally catastrophic. There were fewer farmers, labourers, craftsmen and traders, so agricultural production suffered, leading to severe food shortages.

Other shortages included stone, timber and metal. The epidemic brings about a decline in the commissioning of grand architectural and infrastructure projects, as well as tax revenues. Inflation sets in, trade networks were disrupted, and the economy stagnated.

The prosperity that had characterised the Roman empire for centuries was hit hard.

“The effects of the disease mixed with other things – war, currency debasement, migrations, and civil war – to create a whole cocktail of crisis that ended the Pax Romana,” concludes Elliott.

Professor Colin Elliott is professor of history at Indiana University and the host of the Pax Romana Podcast. He is author of Pox Romana: The Plague that Shook the Roman World (Princeton University Press, 2024). He was speaking to James Osborne on the HistoryExtra podcast.

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