The answer depends on what you mean by “plague.” In the biblical Book of Exodus, the first of the ten plagues of Egypt was the turning of the Nile River into blood. In recorded history, the earliest well-documented plague pandemic struck the Mediterranean in 541 CE. And if you’re asking when the plague bacterium itself first infected humans, the answer goes back roughly 5,000 years, deep into the Bronze Age.
The First Biblical Plague: Water Turned to Blood
In the Exodus narrative, God commands Moses and Aaron to strike the Nile with a staff, turning its waters to blood. The transformation wasn’t limited to the river. According to the text, it extended to streams, reservoirs, and water stored in wooden and stone vessels throughout Egypt. The fish in the Nile died, the water became foul, and Egyptians were forced to dig wells around the riverbank to find drinkable water. The plague lasted seven days.
An ancient Egyptian document known as the Ipuwer Papyrus contains a strikingly similar line: “Indeed, the river is blood, yet men drink of it.” Some scholars have pointed to this as possible independent corroboration of the biblical account, though the papyrus is difficult to date precisely, and others consider it a coincidence of poetic language rather than a historical record of the same event.
The Earliest Plague Infections: 5,000 Years Ago
If you’re asking about the disease we call plague, caused by the bacterium Yersinia pestis, it has been infecting humans far longer than most people realize. The word “plague” itself comes from the Latin plaga, meaning “stroke” or “wound,” and infections are believed to have been common since at least 3000 BCE.
Researchers have extracted Y. pestis DNA from human teeth dating back roughly 5,000 years, found across sites in Eurasia. In Britain, three plague genomes were sequenced from remains approximately 4,000 years old. Two came from a mass burial at Charterhouse Warren in Somerset, and one from a single burial under a stone monument in Levens, Cumbria. These represent the earliest known evidence of plague reaching Britain’s shores.
But these ancient strains were fundamentally different from the plague that later devastated medieval Europe. Early Y. pestis lacked a critical gene that allows the bacterium to survive inside flea guts. Without that gene, the disease could not spread through flea bites, the transmission route behind the great bubonic plague pandemics. Instead, early plague likely spread through respiratory droplets or direct contact. Sometime between 1600 and 950 BCE, the bacterium acquired this gene, gaining the ability to hitch a ride in fleas and sparking a new, far deadlier chapter in human history.
How Early Plague Shaped Ancient Settlements
Archaeological evidence suggests that plague and other zoonotic diseases influenced how early farming communities organized themselves. In what is now west-central Ukraine, a network of enormous Neolithic settlements known as Trypillia mega-sites flourished between roughly 4000 and 3400 BCE. These were some of the largest communities in the world at the time, with thousands of people and livestock living in close quarters.
Researchers have found that strains of Y. pestis dating to this period were circulating in nearby regions of Siberia and northeast Asia. The disease burden from plague and other infections may have driven these communities to abandon their densely packed settlements in favor of smaller, more spread-out villages. Modeling studies suggest that the way houses were clustered within these mega-sites directly affected how fast epidemics could rip through a population, and that dispersing into smaller groups was an effective survival strategy.
The Plague of Athens: 430 BCE
One of the earliest well-documented epidemics in Western history struck Athens in 430 BCE, during the Peloponnesian War. The historian Thucydides, who caught the disease and survived, described a highly contagious illness marked by high fever, a pustular rash, and severe diarrhea. For centuries, scholars debated whether this was smallpox, typhus, or something else entirely. In 2006, researchers extracted ancient DNA from skeletons in an Athenian mass grave and identified genetic material from Salmonella enterica, the bacterium that causes typhoid fever. This finding pointed to typhoid as the likely culprit, though the identification remains debated.
The Antonine Plague: 165 CE
The first major pandemic to sweep the Roman Empire arrived around 165 CE, brought back by soldiers returning from campaigns in Persia. The physician Galen documented the symptoms in detail: fever, skin eruptions that progressed through distinct stages of ulceration and scabbing. For decades, the scholarly consensus held that this was smallpox, based largely on the characteristic progression of the pustules that Galen described.
More recently, that consensus has come under pressure. Galen never mentioned the permanent facial scarring that is smallpox’s most distinctive calling card. And several contemporary writers described humans and animals falling sick simultaneously, something smallpox cannot do since it infects only humans. Some researchers now suggest measles or even an extinct virus as possible alternatives. Whatever the pathogen, it hit a population with no prior immunity. The Roman historian Dio Cassius reported that 2,000 people died in a single day in Rome at the epidemic’s peak. Roman military strength was devastated, with one later account claiming the army was “reduced almost to extinction.”
The Justinianic Plague: The First Bubonic Pandemic
The first confirmed pandemic of bubonic plague, the flea-transmitted form of the disease, began in 541 CE during the reign of the Byzantine Emperor Justinian. Known as the Justinianic Plague or the First Pandemic, it struck the Mediterranean world and recurred in at least 18 documented waves over the following two centuries.
Some scholars believe the outbreak originated in East Africa before reaching the major port city of Constantinople in 542. The contemporary historian Procopius wrote an extensive firsthand account. Estimates of the death toll vary dramatically. Maximalist scholars argue the plague killed between a quarter and half the population of the Eastern Roman Empire, potentially 15 to 100 million people over several years. Constantinople alone may have lost 25 to 50 percent of its residents during the initial outbreak. More conservative assessments, based on analysis of legislation, population data, and archaeological evidence from the period, suggest the demographic impact may have been less catastrophic than the most dramatic ancient accounts imply.
The Justinianic Plague set the stage for the more famous Second Pandemic, which began with the Black Death in 1347 and killed roughly a third of Europe’s population. Both were caused by Yersinia pestis, the same bacterium that had been quietly evolving in rodent populations for thousands of years before acquiring the genetic tools to unleash devastation on a continental scale.