Why do historians disagree about the death toll of the Plague of Justinian?

Historians face significant challenges in determining the death toll of the Plague of Justinian, leading to estimates that range widely from 25 million to 100 million deaths.1

The disagreement stems primarily from the reliance on limited historical records and the difficulty of applying modern statistical analysis to ancient data. Much of the traditional "received wisdom"—which suggested that one-third of Europe’s population perished—is now viewed by many modern medical historians as an exaggeration. Critics argue that these earlier figures were often derived from analogies to the Black Death, a later pandemic for which more comprehensive documentation exists.1

Because the plague occurred in the 6th century, precise demographic data is unavailable, making it impossible to confirm exact mortality rates. While contemporary accounts, such as those by the historian Procopius, provide vivid descriptions of the devastation in cities like Constantinople, extrapolating these localized observations to the entire empire remains a subject of intense scholarly debate.12