Pestilence has shaped human civilizations as profoundly as any war, revolution, or technological breakthrough. From the devastating epidemic that struck Athens in 430 BC to the influenza pandemic that killed an estimated 50 to 100 million people in 1918–1919, outbreaks of infectious disease have toppled empires, redirected economies, and reshaped how societies think about public health. What makes the historical record especially fascinating is how much we are still learning about these events: ancient DNA recovered from mass graves is overturning century-old assumptions about which pathogens were actually responsible for some of history’s most infamous plagues.
The Plague of Athens
One of the earliest well-documented epidemics struck Athens during the Peloponnesian War, beginning around 430 BC and recurring in waves until roughly 427 BC. The historian Thucydides, who contracted the disease himself, left a detailed eyewitness account describing fever, conjunctival inflammation, bloody cough, gastrointestinal symptoms, a spreading rash, and high mortality. His account remains the only primary source, and scholars have spent centuries arguing over what pathogen was responsible.
The list of proposed culprits is long. Researchers have variously pointed to typhoid fever, epidemic typhus, smallpox, measles, bubonic plague, and influenza. One review concluded that, given the nuances of Thucydides’ Greek text, measles was the most likely explanation.1PubMed Central. The cause of the plague of Athens: plague, typhoid, typhus, smallpox, or measles? But molecular evidence has complicated the picture. DNA analysis from dental pulp of skeletons recovered from a mass burial at Athens’ Kerameikos cemetery detected DNA from Salmonella enterica, leading a separate team to propose that an unusually virulent strain of non-typhoidal Salmonella was the true cause.2International Journal of Infectious Diseases. The plague of Athens (430–427 BC): Integration of historical, clinical, and ancient DNA data supports an invasive non-typhoidal Salmonella enterica etiology A more recent review has even raised the possibility that early strains of Yersinia pestis, the plague bacterium, which lacked the flea-borne virulence factors of later strains, could have caused a pneumonic form transmitted directly between people.3PubMed. A plague like no other: beyond the buboes in Thucydides’ account of the Plague of Athens
The honest answer is that we still do not know for certain what struck Athens. That uncertainty itself is instructive: a single ancient text, however vivid, can match the symptom profiles of multiple diseases, and even ancient DNA findings from a handful of skeletons are open to debate. What is not in doubt is the scale of the catastrophe. The epidemic killed a large share of Athens’ population, including the statesman Pericles, and weakened the city during a critical phase of its war with Sparta.
The Antonine Plague and the Roman Empire
In the second century AD, the Roman Empire experienced a prolonged epidemic known as the Antonine Plague, which many historians believe was caused by smallpox. Returning soldiers carried it from campaigns in the Near East beginning around 165 AD, and the disease spread across the empire over the following two decades. The physician Galen left descriptions of the illness, though his account is less systematic than Thucydides’ earlier narrative.
The debate around the Antonine Plague centers less on symptoms and more on consequences. Most scholars agree the impact was severe, affecting military recruitment, agricultural output, and state finances.4PubMed. The Antonine Plague and the decline of the Roman Empire Some argue the plague created conditions that contributed to the eventual decline and fall of the Western Roman Empire centuries later. Economic evidence from Roman Egypt suggests the mortality crisis triggered shocks to wages and prices, and that the resulting population loss contributed to a decrease in the return on land and a rise in real wages for surviving workers over the following century.5Journal of Roman Archaeology. A model of demographic and economic change in Roman Egypt after the Antonine plague That pattern of labor scarcity boosting wages for survivors would repeat in later pandemics, most dramatically after the Black Death.
The Justinianic Plague and the First Pandemic
The first historically confirmed pandemic of bubonic plague began in 541 AD within the Eastern Roman (Byzantine) Empire and is named after Emperor Justinian I, who reportedly contracted the disease but survived. The plague swept across the Mediterranean world and continued in recurrent waves until roughly 750 AD, a period scholars call the First Pandemic.6PubMed Central. Ancient Yersinia pestis genomes from across Western Europe reveal early diversification during the First Pandemic (541-750)
For years, historians debated whether Yersinia pestis was truly the cause, since early medieval descriptions of symptoms can be ambiguous. Ancient DNA analysis settled the question. By extracting and sequencing Y. pestis DNA from skeletal remains in an early medieval cemetery, researchers confirmed unambiguously that the bacterium was responsible and placed the strain on a specific branch of the Y. pestis family tree.7PLOS Pathogens. Yersinia pestis DNA from Skeletal Remains from the 6th Century AD Reveals Insights into Justinianic Plague The Justinianic Plague is estimated to have killed tens of millions of people and is widely considered one of the factors behind the decline of Byzantine power in the Mediterranean.
The Black Death
No outbreak looms larger in European memory than the Black Death, which arrived around 1347 and killed roughly a third to half of Europe’s population within a few years. This was the opening act of the Second Pandemic of Y. pestis, which would continue to produce major outbreaks in Europe for centuries. Research into the economic aftermath has found that the initial effects were highly disruptive: wages and per capita income rose sharply as labor became scarce. But the longer-term story varied by region. In some parts of Europe, real wages stayed elevated; in others, they did not.8Journal of Economic Literature. The Economic Impact of the Black Death
The indirect consequences of the Black Death may have been even more significant than the immediate mortality. Historians have linked it to the demise of serfdom in Western Europe, a decline in the authority of religious institutions, the emergence of stronger centralized states, and a long-term shift in economic power toward northwestern Europe. Some scholars see it as a contributing factor in the so-called Great Divergence, the process by which Europe pulled ahead of Asia and the Middle East economically in the centuries that followed.
Climate played a role that researchers are still unpacking. One study found evidence that plague was repeatedly reintroduced into European harbors from animal reservoirs in Asia, with a delay of about 15 years following climate fluctuations, and that there was no support for the idea that plague maintained permanent reservoirs within medieval Europe itself.9PubMed Central. Climate-driven introduction of the Black Death and successive plague reintroductions into Europe The relationship between climate, animal hosts, and plague transmission is complex, though, and does not follow a simple formula linking rainfall patterns to outbreaks across different regions.10PubMed Central. The role of reservoir species in mediating plague’s dynamic response to climate
The Black Death also left a mark on the human genome. By analyzing ancient DNA from individuals who lived before, during, and after the plague in London and Denmark, researchers identified genetic variants near immune-related genes that appear to have been positively selected during the pandemic. The strongest candidate, a variant near the gene ERAP2, is associated with better ability to control Y. pestis inside immune cells. People carrying the protective allele were more likely to survive, and the frequency of that allele increased measurably in the post-plague population.11Nature. Evolution of immune genes is associated with the Black Death
The Columbian Exchange and Epidemic Collapse in the Americas
When Europeans arrived in the Americas after 1492, they brought with them a suite of infectious diseases to which Indigenous populations had no prior exposure. Smallpox, measles, influenza, and typhus swept through the continents, contributing to what was arguably the largest demographic catastrophe in human history. Estimates vary widely, but many scholars believe that 50 to 90 percent of the pre-contact population of the Americas died within the first century or so of European arrival.
The Columbian Exchange was not a single epidemic but an ongoing process of disease transfer alongside the exchange of food crops, technologies, and ideas.12American Economic Association (Journal of Economic Perspectives). The Columbian Exchange: A History of Disease, Food, and Ideas Specific outbreaks within this larger process have their own mysteries. One of the most devastating struck Mexico from 1545 to 1550, an epidemic the Nahua people called “cocoliztli.” Its cause was debated for more than a century, with smallpox long considered the prime suspect. Then, in a breakthrough of ancient pathogen genomics, researchers recovered genome-wide data for Salmonella enterica serovar Paratyphi C from individuals buried in an epidemic-era cemetery at Teposcolula-Yucundaa in Oaxaca, suggesting a bacterial cause of enteric fever rather than smallpox.13Nature Ecology & Evolution. Salmonella enterica genomes from victims of a major sixteenth-century epidemic in Mexico Further analysis has supported the view that this mortality crisis was likely multicausal and associated with a severe megadrought that compounded the effects of infection.14Current Biology. Ancient Pathogen Genomics
Wartime Typhus
If plague defined the medieval world, epidemic typhus was the great wartime pestilence. Caused by the bacterium Rickettsia prowazekii and transmitted by body lice, typhus thrives wherever crowding, filth, and poverty concentrate human bodies without the means to wash or change clothes. It is one of the oldest pestilential diseases known and has arguably determined the outcome of more wars than soldiers and generals ever did.15PubMed. The History of Epidemic Typhus
The most famous military example is Napoleon’s 1812 invasion of Russia. The Grande Armée entered Russia with over 600,000 soldiers and returned with a fraction of that number. While the Russian winter gets most of the blame in popular memory, disease killed far more soldiers than combat. Analysis of skeletal remains from a mass grave in Vilnius, Lithuania, found that louse-borne infections affected close to a third of the soldiers buried there, pointing to typhus and related diseases as a major factor in the French retreat.16PubMed. Evidence for louse-transmitted diseases in soldiers of Napoleon’s Grand Army in Vilnius Typhus continued to ravage armies during the Crimean War, the American Civil War, World War I, and the concentration camps of World War II, where it killed Anne Frank among countless others.
Cholera and the Birth of Epidemiology
Cholera, caused by the bacterium Vibrio cholerae, became a global menace in the nineteenth century as faster trade routes carried the disease from its endemic heartland in South Asia across the world. Seven major cholera pandemics have been recorded since 1817, and the disease still kills tens of thousands of people annually in regions without reliable access to clean water.
Cholera’s place in the history of pestilence is inseparable from the story of John Snow. During the 1854 Broad Street outbreak in London, Snow meticulously mapped cases and traced the epidemic to a contaminated public water pump, establishing that cholera was waterborne at a time when most physicians blamed “bad air,” or miasma. His work laid the foundational principles of modern epidemiology and led directly to major urban sanitation reforms, including centralized water treatment and sewage systems.17PubMed Central. John Snow, Cholera, the Broad Street Pump; Waterborne Diseases Then and Now You can draw a direct line from Snow’s investigation to the municipal water infrastructure that cities worldwide rely on today.
The 1918 Influenza Pandemic
The so-called “Spanish flu” of 1918–1919 remains the benchmark against which modern pandemic preparedness is measured. The virus appeared nearly simultaneously around the world and killed an estimated 50 to 100 million people at a time when the global population was roughly 1.8 billion.18PubMed Central. The 1918 Influenza Pandemic and Its Legacy It struck in three waves, with the second wave in the autumn of 1918 being by far the deadliest.
One of the most puzzling features of the 1918 pandemic was its age-specific mortality. Unlike typical influenza, which hits the very young and the very old hardest, the 1918 virus killed young adults at extraordinary rates. Using historical records from Canada and the United States, researchers identified a peak of mortality at the exact age of 28 and proposed a striking explanation: people born around 1890 would have been infants or very young children during the Russian flu pandemic of 1889–1890. Early-life exposure to that earlier influenza virus may have primed their immune systems in a way that backfired catastrophically when they encountered the antigenically different 1918 strain, producing a dysregulated and ultimately lethal immune response.19PLOS ONE. Age-Specific Mortality During the 1918 Influenza Pandemic: Unravelling the Mystery of High Young Adult Mortality The idea that an immune system’s memory of one pathogen can actually make a later encounter with a related pathogen worse has implications far beyond 1918, and remains an active area of research in immunology.
Livestock Pestilence and Rinderpest
Pestilence is not exclusively a human story. Rinderpest, a viral disease of cattle and other cloven-hoofed animals, was historically one of the most devastating animal diseases known, frequently causing mortality approaching 100 percent in susceptible herds and triggering catastrophic famine and political instability in affected regions.20PubMed Central. Global rinderpest eradication: lessons learned and why humans should celebrate too In sub-Saharan Africa during the 1890s, a rinderpest epizootic wiped out vast herds of cattle and wild ungulates, causing widespread starvation and destabilizing communities. In 2011, rinderpest became only the second disease in history, after smallpox, to be officially declared eradicated. The campaign to eliminate it relied on coordinated vaccination drives across dozens of countries and stands as one of veterinary medicine’s greatest achievements.
How Quarantine Evolved
The repeated devastation of plague forced Mediterranean societies to develop some of the earliest organized public health systems. By the fifteenth century, cities like Venice had established lazarettos, initially as hospitals for plague victims and later as centers for quarantine and disinfection of incoming travelers and goods.21Kent Academic Repository. The Control of Plague in Venice and Northern Italy 1348-1600 These institutions, managed by the health magistracies of different cities, formed a transnational plague-prevention system across the Mediterranean, with ships and merchants required to undergo inspection and isolation before entering ports.22Social History of Medicine. Materiality, Quarantine and Contagion in the Early Modern Mediterranean
The word “quarantine” itself derives from the Italian “quarantina,” referring to the 40-day isolation period that Venice imposed on arriving ships during plague outbreaks. The principle of isolating the sick and those exposed to disease eventually evolved into the formal public health apparatus of the modern era. Centuries later, a refinement of this concept, ring vaccination, proved critical to the eradication of smallpox. Rather than trying to vaccinate entire populations, health workers focused on rapidly diagnosing infectious cases and vaccinating all direct contacts, a strategy that could contain an epidemic when cases were identified quickly enough.23PubMed Central. Ring vaccination and smallpox control
What Ancient DNA Is Rewriting
Running through many of these examples is a quiet revolution: the ability to extract and sequence pathogen DNA from centuries-old and even millennia-old human remains. Researchers now have near-complete ancient genome sequences for bubonic plague, smallpox, cholera, tuberculosis, leprosy, and syphilis, among others.24Current Biology. Pathogens on the road to history: paleogenomics of infectious disease in the ancient and historical human record Advances in metagenomic techniques have made it possible to recover highly fragmented DNA molecules from ancient biological samples, track pathogen evolution over large timescales, and reconstruct distribution patterns that historical texts alone could never reveal.25PubMed. Insights into infectious diseases through ancient pathogen genomics
This work does more than satisfy historical curiosity. Ancient pathogen genomes, combined with archaeological and historical data, provide a temporal and behavioral context for health in the past that is directly relevant to challenges facing the world today, including the emergence of novel pathogens.26PubMed Central. Ancient pathogens provide a window into health and well-being Understanding how a pathogen evolved virulence factors, jumped between host species, or responded to human population changes can inform how we model the risks of future spillover events.
Permafrost, Climate Change, and the Next Chapter
One concern that regularly surfaces in popular media is the idea that thawing permafrost in the Arctic could release ancient frozen pathogens and trigger new epidemics. Permafrost in Arctic and subarctic regions is known to harbor metabolically active microbes, including potentially harmful organisms that have survived for thousands of years, and atmospheric transport could theoretically carry released organisms over long distances.27Environmental Research Letters. Potential One Health risk of downwind exposure to airborne pathogens from thawing Siberian permafrost The scenario is not entirely hypothetical: a 2016 anthrax outbreak in Siberia was linked to a thawed reindeer carcass.
That said, recent assessments have cooled the more dramatic versions of this fear. Based on current knowledge, the risk posed by viruses emerging from thawing permafrost appears to be no greater than the risk posed by viruses already present in temperate soils and aquatic systems.28PubMed Central. Cooling perspectives on the risk of pathogenic viruses from thawing permafrost The far more pressing concern for future pandemics is the familiar one: habitat destruction and climate change pushing wildlife and human populations into closer contact, creating fresh opportunities for pathogens to jump species. History suggests that the next great pestilence is more likely to emerge from a wet market, a deforested frontier, or an intensively farmed animal population than from a melting glacier.