The Plague of Justinian was the first major bubonic plague pandemic recorded in Europe, and was the first pandemic to ever be described or documented with any relative reliability. The plague takes its name from Emperor Justinian I, who ruled the Byzantine Empire (Eastern Roman Empire) at the time of the outbreak. The Byzantine capital of Constantinople (also known then as Byzantium, and Istanbul today) was the hardest hit city during the pandemic, and where the majority of sources are from. Until recently, it was only assumed that the outbreak was bubonic plague, due to the symptoms described by contemporary historians, but scientists were able to confirm that it was in fact Yersinia pestis (the bacterium that causes plague) in 2013. Constantinople overwhelmed It is thought that the plague was brought to Constantinople by Egyptian grain merchants, although a recent theory suggests it was brought from the Eurasian Steppes (from where Yersinia pestis originates) to Europe by Hunnic tribes. While the exact origins of the plague remain unclear, it is estimated that up to 300,000 people died in Constantinople in the first year of the outbreak. Contemporary sources claim that there were approximately 5,000 deaths in the city every day at the height of the pandemic, even reaching highs of 10,000 on some days. Constantinople outbreak was unique A 2019 study, conducted by researchers from Jerusalem and Princeton raises some important questions about the scale of the outbreak across Europe. They dispute the claim by some modern historians that this pandemic killed up to half of the population of the Mediterranean (or that it was instrumental to the collapse of the Eastern Roman Empire), instead suggesting that the scale of the outbreak in Constantinople was unique to that city. They use a variety of literary, archeological, and scientific sources to show that the plague was unlikely to have reached this magnitude across other cities at the time, nor did it spread in the same way that the Black Death did six centuries later. While future studies are likely to provide further insight into these theories, it is important to remember this contrasting hypothesis when studying pre-2019 sources.

The Plague of Justinian was an outbreak of bubonic plague that ravaged the Mediterranean and its surrounding area, between 541 and 767CE. It was likely the first major outbreak of bubonic plague in Europe, and possibly the earliest pandemic to have been recorded reliably and with relative accuracy. Contemporary scholars described the symptoms and effects of the disease in detail, and these matched descriptions of the Black Death and Third Pandemic, leading most historians to believe that this was bubonic plague. It was also assumed that the plague originated in sub-Saharan Africa, before making its way along the Nile to Egypt, and then across the Mediterranean to Constantinople. In 2013, scientists were able to confirm that Justinian's Plague was in fact Yersinia pestis (the bacteria which causes bubonic plague), and recent theories suggest that the plague originated in the Eurasian Steppes, where the Black Death and Third Pandemic are also thought to have originated from, and that it was brought to Europe by the Hunnic Tribes of the sixth century. Plague of Justinian The pandemic itself takes its name from Emperor Justinian I, who ruled the Byzantine Empire (or Eastern Roman Empire) at the time of the outbreak, and who actually contracted the disease (although he survived). Reports suggest that Constantinople was the hardest hit city during the pandemic, and saw upwards of five thousand deaths per day during the most severe months. There are a multitude of sources with differing estimates for the plague's death toll, with most ranging between 25 and 100 million. Until recently, scholars assumed that the plague killed between one third and 40 percent of the world's population, with populations in infected regions declining by up to 25 percent in early years, and up to 60 percent over two centuries. The plague was felt strongest during the initial outbreak in Constantinople, however it remained in Europe for over two centuries, with the last reported cases in 767. Pre-2019 sources vary in their estimates, with some suggesting that up to half of the world's population died in the pandemic, while others state that it was just a quarter of the Mediterranean or European population; however most of them agree that the death toll was in the tens of millions. Historians have also argued about the plague's role in the fall of the Roman Empire, with opinions ranging from "fundamental" to "coincidental", although new evidence is more aligned with the latter theories. Challenging theories As with the recent studies which propose a different origin for the disease, one study conducted by researchers in Princeton and Jerusalem calls into question the accuracy of the death tolls estimated by historians in the 19th and 20th centuries. In 2019, L. Mordechai and M. Eisenberg published a series of papers suggesting that, although the plague devastated Constantinople, it did not have the same impact as the Black Death. The researchers argue that modern historians have taken a maximalist approach to the death tolls of the pandemic, and have applied the same models of distribution to Justinian's Plague as they believe occurred during the Black Death; however there is little evidence to support this. They examine the content and number of contemporary texts, as well archaeological, agricultural and genetic evidence which shows that the plague did spread across Europe, but did not seem to cause the same societal upheaval as the Black Death. It is likely that there will be further investigation into this outbreak in the following years, which may shed more light on the scale of this pandemic.