The first recorded pandemic is the Plague of Justinian, which struck in AD 541 and recurred in waves across western Eurasia and North Africa for roughly two centuries, until around AD 750. While earlier outbreaks like the Antonine Plague (AD 165) and the Plague of Athens (430 BC) devastated large populations, the Plague of Justinian is the earliest disease event with confirmed genomic evidence of a single pathogen spreading across multiple continents.
Why the Plague of Justinian Holds the Title
A pandemic, in epidemiological terms, is an epidemic that spreads to multiple continents. That distinction matters because the ancient world saw plenty of devastating outbreaks that stayed regional. The Plague of Justinian meets the threshold clearly: it spread across the Mediterranean, into western and central Europe, North Africa, and possibly central Asia and East Africa. It caused tens of millions of deaths across these regions over its roughly 200-year span of recurring waves.
The disease first appeared in the historical record at Pelusium, a port city in what is now northeastern Egypt, before spreading throughout the Eastern Roman (Byzantine) Empire. For centuries, historians debated what actually caused it. That question was finally settled in 2025, when researchers at the University of South Florida and Florida Atlantic University extracted DNA from a mass grave at the ancient city of Jerash in Jordan. The genomic analysis confirmed the pathogen was Yersinia pestis, the bacterium responsible for plague. Victims buried between AD 550 and 660 carried nearly identical strains, providing the first direct molecular proof that this specific bacterium drove the pandemic within the Byzantine Empire.
Yersinia pestis is the same species behind the Black Death of the 14th century, though genetic analysis shows the Justinianic strain was distinct. Both emerged separately from wild rodent reservoirs, likely carried to human populations by fleas.
What About the Antonine Plague?
The Antonine Plague, which began around AD 165 and lasted roughly 15 to 20 years, is sometimes called the first pandemic, but most historians classify it as something slightly different. It ravaged the Roman Empire extensively, yet it largely stayed within the empire’s borders rather than spreading independently across multiple continents. It also predates any confirmed genomic identification of its pathogen, which means we still don’t know for certain what caused it.
The leading suspect is smallpox, based on written descriptions of symptoms from the physician Galen. Smallpox-like rashes have been found on Egyptian mummies dating back roughly 3,000 years, and the earliest written description of a smallpox-like disease appeared in China in the 4th century CE. But no laboratory confirmation exists for the Antonine Plague specifically.
The death toll remains fiercely debated. Ancient sources are dramatic: the Roman historian Cassius Dio reported that 2,000 people often died in Rome in a single day around AD 189. Modern estimates vary wildly depending on the scholar. Conservative calculations suggest mortality was only 1 to 2 percent above normal, translating to roughly 500,000 to 1 million additional deaths. More recent modeling, however, places the figure much higher. One widely cited estimate puts overall mortality at 22 to 24 percent of the empire’s population, potentially exceeding 25 percent if birth rates dropped afterward. Historian Kyle Harper’s more moderate estimate suggests the hardest-hit areas saw about a 20 percent increase in mortality, with the empire-wide average closer to 8 to 10 percent.
How the Antonine Plague Reshaped Rome
Regardless of the exact death toll, the Antonine Plague’s consequences were enormous. It hit the Roman military hard, making it difficult to maintain troop levels along the empire’s vast borders. Agricultural labor dried up, the urban economy contracted, and state revenues plummeted. The empire’s weakened borders and depleted military opened the door for neighboring groups to push inward. Rome began recruiting soldiers from these same populations, accelerating cultural and political shifts that many historians see as early steps toward the empire’s eventual collapse in the West in the 5th century.
Earlier Outbreaks That Don’t Qualify
The Plague of Athens in 430 BC is one of the most famous disease events in ancient history, but it was not a pandemic. It struck during the Peloponnesian War and lasted about four years, confined largely to southern Greece. The word “plague” in ancient texts didn’t refer specifically to bubonic plague. It was a general term for any severe pestilence. Historians have proposed typhoid, typhus, smallpox, and measles as possible causes, but none has been confirmed. Because the outbreak stayed regional, it’s classified as an epidemic rather than a pandemic.
Even further back, there’s intriguing evidence of widespread plague long before written records. Genomic analysis of ancient human remains has detected Yersinia pestis in people who lived roughly 5,000 to 5,300 years ago, during the late Stone Age. At least three distinct lineages of the bacterium have been found in remains scattered across Eurasia, from Latvia to Sweden to the Caucasus and Altai mountain regions. The period between 6,000 and 4,000 years ago appears to have been critical for the evolution of plague as a human pathogen. Whether these ancient infections constituted a pandemic is impossible to say. There are no written records, no way to estimate how far the disease spread through populations, and no way to calculate mortality. They remain tantalizing hints of prehistoric outbreaks we may never fully understand.
How the Answer Depends on the Definition
If you define “first pandemic” strictly, requiring confirmed multi-continental spread with genomic evidence of the pathogen, the Plague of Justinian (AD 541) is the answer. If you loosen the definition to include any empire-wide catastrophic outbreak described in historical sources, the Antonine Plague (AD 165) has a reasonable claim. And if you’re willing to go even further, looking at genetic traces in ancient bones, plague bacteria were infecting humans across Eurasia more than 5,000 years ago, though we can’t call those events pandemics with any certainty.
The distinction isn’t just academic. Each of these events shaped the civilizations that followed them, redrawing borders, collapsing economies, and shifting the balance of power across continents. The Plague of Justinian weakened the Byzantine Empire’s grip on its territories. The Antonine Plague may have set Rome on its long path toward decline. The unnamed Stone Age outbreaks potentially influenced population movements across prehistoric Europe and Asia. What we call “the first pandemic” depends on how much evidence we require, but the consequences of these ancient diseases rippled forward for centuries.