The Plague of Justinian was a devastating pandemicAn infectious disease that spreads across a very wide area, often affecting the entire known world. that struck the Byzantine Empire and much of the known world beginning in 541 CE. It is considered to be the first clearly recorded outbreak of bubonic plague in history and one of the deadliest pandemics ever to affect humanity. The plague is named after the Byzantine Emperor Justinian I, who ruled the empire at the time and who himself contracted the disease, though he survived.
What Was the Byzantine Empire?
The Byzantine Empire, also known as the Eastern Roman Empire, was the continuation of the Roman Empire in the eastern part of Europe and the Middle East after the fall of the Western Roman Empire in 476 CE. Its capital was the city of Constantinople, which is known today as Istanbul in modern-day Turkey. The Byzantine Empire was one of the most powerful and wealthy states in the world during the Early Middle Ages and served as an important center of Christian civilization, trade, and culture for many centuries. In fact, at the time of the Plague of Justinian, Constantinople was the largest and most important city in the Mediterranean world. The emperor ruling the Byzantine Empire at the time of the plague was Justinian I, who reigned from 527 to 565 CE and had ambitious plans to reunite the old Roman Empire under his rule. As such, the Plague of Justinian struck at a particularly important moment in the history of the Byzantine Empire and the broader world.
FactsthatCrunchJustinian I ruled the Byzantine Empire from 527 CE to 565 CE and launched ambitious military campaigns that recaptured much of Italy and North Africa, bringing the empire close to reuniting the old Roman world. The Plague of Justinian struck during his reign, killing enormous numbers of soldiers and farmers, collapsing government tax income, and badly setting back the territorial gains his armies had fought to secure.
What Was the Plague of Justinian?
The Plague of Justinian was a pandemic caused by the bacteriumA tiny single-celled living thing that can cause disease in humans and animals. Yersinia pestisThe specific germ that caused both the Plague of Justinian and the later Black Death., which is the same bacterium responsible for the Black Death that devastated Europe in the 14th century. A pandemic is the term used to describe the spread of an infectious disease over a very wide area, often affecting the entire known world. In general, historians consider the Plague of Justinian to be the first pandemic in recorded history. The disease caused bubonic plagueA deadly disease causing swollen lymph nodes, fever, chills, and disorientation, with a mortality rate of 60 to 80 percent without modern medicine., which was a horrifying and extremely deadly disease that caused swollen lymph nodes, fever, chills, and disorientation in those who contracted it. Without modern medicines such as antibioticsModern medicines that kill bacteria and that did not exist during the time of the Plague of Justinian., bubonic plague killed the majority of the people it infected, with some estimates suggesting a mortality rateThe share of sick people who die from a particular disease. of between 60 and 80 percent for those who became sick.
For many centuries historians were uncertain exactly what disease caused the Plague of Justinian. In reality, it was not until 2013 that scientists were able to use DNA analysis of ancient human remains from burial sites across the former Byzantine Empire to confirm that the plague was indeed caused by Yersinia pestis. This discovery was important because it confirmed the connection between the Plague of Justinian and the later Black Death, showing that both pandemics were caused by the same disease.
Origins and Spread of the Plague
Historians believe the Plague of Justinian likely originated in Central Asia, possibly in the region of the Tian Shan mountains on the borders of modern-day Kyrgyzstan, Kazakhstan, and China. From there, the disease traveled along trade routes to reach Egypt, which was at the time the main supplier of grain to the Byzantine Empire. The first recorded outbreak of the plague occurred in the port city of Pelusium in Egypt in 541 CE. From Egypt, the plague spread rapidly through the trade networks of the Byzantine Empire, carried primarily by black rats that traveled aboard the grain ships that constantly moved food and goods around the Mediterranean Sea. For example, rats were attracted to the vast grain stores kept in the warehouses of Constantinople and other major port cities, and the fleas that lived on these rats carried the bacteria responsible for the plague.
The plague reached Constantinople itself in 542 CE and hit the city with devastating force. The Byzantine historian Procopius, who lived in Constantinople during the outbreak, recorded that at the peak of the epidemic the city was losing thousands of people every single day. So many people died so quickly that the bodies could not be buried fast enough. As well, burial sites filled up, workers tasked with moving the dead died themselves on the job, and Emperor Justinian was forced to order mass graves to be dug outside the city walls. The markets, courts, schools, and workshops of Constantinople came to a complete standstill. For instance, modern historians estimate that the plague killed somewhere between 20 and 40 percent of the population of Constantinople during the initial outbreak. In all, the plague spread from Constantinople across the entire Mediterranean world, reaching as far north as Britain and Denmark and as far east as the Arabian Peninsula.
FactsthatCrunchNow the disease in Byzantium ran a course of four months, and its greatest virulence lasted about three. And at first the deaths were a little more than the normal, then the mortality rose still higher, and afterwards the tale of dead reached five thousand each day, and again it even came to ten thousand and still more than that. During that time it seemed no easy thing to see any man in the streets of Byzantium, but all who had the good fortune to be in health were sitting in their houses, either attending the sick or mourning the dead.
Procopius was living in Constantinople when the plague struck the city in 542 CE, and he recorded what he saw in his official history of Justinian's wars.
Impact of the Plague on the Byzantine Empire
The impact of the Plague of Justinian on the Byzantine Empire was enormous and far-reaching. For example, one of the most immediate effects was the devastating loss of life among the farming population. The Byzantine economy was heavily dependent on agriculture and taxation, and with so many farmers dead, fields were left empty and food production collapsed. As a result, famines followed the plague in 542 and again in 545 and 546 CE, making an already terrible situation even worse. At the same time, the loss of so many taxpayers caused the government’s income to collapse, making it impossible for Justinian to fund his ambitious military campaigns and building projects.
In fact, the plague struck the Byzantine Empire at one of the most critical moments in its history. At the time the plague first appeared, Justinian’s armies had already successfully recaptured much of Italy and North Africa and were very close to reuniting the core of the old Roman Empire under Byzantine rule. With that said, the plague killed enormous numbers of soldiers and disrupted the supply lines that kept the armies fed and equipped. As such, the military campaigns that had seemed on the verge of success were badly set back, and many of the territories that Justinian had worked so hard to recapture were eventually lost again in the decades that followed.
The plague did not disappear after the first outbreak. In reality, it returned in waves repeatedly for more than two centuries, continuing to strike different parts of the Byzantine Empire and the surrounding world until approximately 750 CE. Each new wave of the disease killed more people and made it harder for the empire to recover its strength. For instance, historians believe that the long-term weakening of the Byzantine Empire caused by the repeated outbreaks of plague was an important factor in explaining why the empire was unable to resist the rapid expansion of Arab Muslim forces in the 7th century, which resulted in the loss of Egypt, Syria, and other major territories.
FactsthatCrunchSignificance of the Plague of Justinian
The Plague of Justinian is one of the most significant events of the Early Middle Ages and one of the most devastating pandemics in all of human history. Historians estimate that the total death toll from the plague and its recurring waves may have reached as high as 25 to 50 million people across Europe, the Middle East, and North Africa, though the exact figures are debated. In general, the plague is considered to have permanently reduced the population of the eastern Mediterranean world for generations.
Furthermore, some historians consider the Plague of Justinian to be a dividing line between the ancient world and the beginning of the Middle Ages, as it helped bring the era of late antiquityThe period of ancient history before the Middle Ages, associated with civilizations like Rome and Greece. to a close by weakening the Byzantine Empire’s ability to maintain the traditions and institutions of the old Roman world. As stated above, the same bacterium that caused the Plague of Justinian also caused the Black Death in the 14th century, making these two catastrophic pandemics deeply connected events in history. As such, the Plague of Justinian is a vital event for students to understand not only because of the enormous suffering it caused at the time, but also because of the long shadow it cast over the history of the Middle Ages and beyond.
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Key Vocabulary
Pandemic
Bacterium
Yersinia pestis
Bubonic plague
Mortality rate
Antiquity
Antibiotics
Frequently Asked Questions
When did the Plague of Justinian happen?
The Plague of Justinian began in 541 CE and first reached Constantinople in 542 CE. It did not end quickly, however, and returned in waves for more than two centuries. These outbreaks continued to strike the Byzantine Empire until about 750 CE.
What caused the Plague of Justinian?
The plague was caused by the bacterium Yersinia pestis, the same germ that later caused the Black Death. The disease spread through fleas that lived on black rats. These rats traveled aboard grain ships that moved food around the Mediterranean Sea. Scientists confirmed the cause in 2013 through DNA analysis of ancient remains.
How many people died in the Plague of Justinian?
Historians estimate that the plague and its repeated waves may have killed 25 to 50 million people. This death toll spread across Europe, the Middle East, and North Africa. In Constantinople alone, the first outbreak killed between 20 and 40 percent of the population. The exact numbers are still debated today.
Why is the plague named after Justinian?
The plague is named after Emperor Justinian I, who ruled the Byzantine Empire when the outbreak struck. He reigned from 527 to 565 CE and even caught the disease himself, though he survived. At the time, he was close to reuniting the old Roman Empire under his rule. The plague badly set back these ambitious plans.
How did the plague affect the Byzantine Empire?
The plague killed huge numbers of farmers, which caused food production to collapse and led to famines. The loss of taxpayers also cut government income, so Justinian could not fund his armies. Many lands his armies had recaptured were later lost again. The repeated outbreaks left the empire too weak to resist Arab expansion in the 7th century.
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MLA: Millar, B. “Plague of Justinian: A Detailed Summary.” HistoryCrunch, 17 October 2026, https://historycrunch.com/plague-of-justinian/.
APA: Millar, B. (2026). Plague of Justinian: A Detailed Summary. HistoryCrunch. https://historycrunch.com/plague-of-justinian/
Chicago: Millar, B. “Plague of Justinian: A Detailed Summary.” HistoryCrunch. October 17, 2026. https://historycrunch.com/plague-of-justinian/
Sources
- Barbara Rosenwein, A Short History of the Middle Ages.
- Fordham Medieval Sourcebook
