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One Of The Worst Pandemics In History Perhaps Wasn't As Severe As Thought


Tom Hale

Tom is a writer in London with a Master's degree in Journalism whose editorial work covers anything from health and the environment to technology and archaeology.

Senior Journalist

Emperor Justinian flanked by archbishop Maximian from the 6th century mosaic. Michal Szymanski/Shutterstock

The Plague of Justinian is one of the worst pandemics in human history, often thought to have wiped out around half of the population of the Eastern Roman Empire. Although this disease outbreak certainly caused a colossal amount of death and misery, a new study in the journal PLOS One suggests the death rate and severity were perhaps not as widespread as previously assumed.

The pathogen that was responsible for the Justinianic Plague was Yersinia pestis, the same bacterium behind the Black Death in the 14th century, which lept from port to port across the Mediterranean Sea with the help of hitchhiking rats and fleas. 


The plague broke out in Egypt and took root in the Eastern Roman Empire (aka the Byzantine Empire) between 541 to 542 CE, with later waves recurring as late as 750 CE. Cases of the disease were reported in cities and villages as far-flung as Northern Europe, the Middle East, and North Africa, but the hardest-hit area was the city of Constantinople in present-day Turkey.

Here in the empire’s capital, some written documents suggest the plague killed up to 300,000 people in the city, over half of the population at the time. Previous attempts to understand the Plague of Justinian have often relied on these primary sources to piece together the rest of the puzzle. However, this new research suggests Constantinople's run-in with the disease might not necessarily reflect the whole picture.

Recent mathematical modeling by the University of Maryland suggests the impact of the pandemic might have been overstated. While the precise death toll is still unclear, their findings indicate that the outbreak's death count is often based on primary sources from Constantinople, where the outbreak was well-documented but also more severe. Further afield, it's unlikely the outbreak was as severe since the transmission routes would vary across the diverse empire. 

For example, the disease is more likely to spread in a densely populated city linked to extensive trade routes, compared to backwater settlements in Northern Europe. Unfortunately, these types of locations are also less likely to have detailed and accurate written records. But even among different cities, each with their own ecological environment and social structures, the researchers believe the outbreak is unlikely to have unfolded as severely as written sources from Constantinople indicate. 


"Our results strongly suggest that the effects of the Justinianic Plague varied considerably between different urban areas in late antiquity," study co-author Lee Mordechai, an environmental historian and a postdoctoral fellow at the University of Maryland's National Socio-Environmental Synthesis Center (SESYNC), said in a statement.

"This is the first time, to our knowledge, that a robust mathematical modeling approach has been used to investigate the Justinianic Plague," said lead author Lauren White, PhD, a quantitative disease ecologist at SESYNC. "Given that there is very little quantitative information in the primary sources for the Justinianic Plague, this was an exciting opportunity to think creatively about how we could combine present-day knowledge of plague's etiology with descriptions from the historical texts."


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