Infectious disease modeling study casts doubt on the impact of Justinian plague

Many have claimed that the Justinian plague (c. 541-750 CE) killed half the population of the Roman Empire. Historical research and the mathematical model now challenge the death rate and severity of this first plague pandemic.

Researchers Lauren White, Ph.D. and Lee Mordechai, Ph.D., from the National Center for Socioenvironmental Synthesis (SESYNC) at the University of Maryland, examined the impacts of the Justinian plague using mathematical models. Using modern plague research as a basis, the two developed new mathematical models to reexamine the primary sources from the time of the Justinian plague outbreak. From the model, they discovered that it was unlikely that any route of plague transmission would have had both the death rate and duration described in the primary sources. Their findings appear in an article titled “Modeling the Justinian Plague: Comparing Hypothetical Transmission Routes” in MORE ONE.

“This is the first time that we know of that a robust mathematical modeling approach has been used to investigate the Justinian plague,” said lead author Lauren White, Ph.D., a quantitative disease ecologist and postdoctoral fellow at SESYNC. “Given that there is very little quantitative information in the primary sources of the Justinian plague, this was an exciting opportunity to think creatively about how we might combine current knowledge of the plague aetiology with descriptions from historical texts.”

White and Mordechai focused their efforts on the city of Constantinople, capital of the Roman Empire, which had a relatively well-described outbreak in 542 CE. Some primary sources claim that the plague killed up to 300,000 people in the city, which had a population of about 500,000 people at the time. Other sources suggest that the plague killed half of the empire’s population. Until recently, many scholars accepted this image of mass death. By comparing the combined bubonic, pneumonic, and transmission routes, the authors showed that no single transmission route accurately mimicked the outbreak dynamics described in these primary sources.

Existing literature often assumes that the Justinian plague affected all areas of the Mediterranean in the same way. The new findings in this paper suggest that given the variation in ecological and social patterns across the region (for example, climate, population density), a plague outbreak is unlikely to have impacted all corners of the diverse empire by same.

“Our results strongly suggest that the effects of the Justinian plague varied considerably between different urban areas in late antiquity,” said co-author Lee Mordechai, an environmental historian and postdoctoral fellow at SESYNC when writing the article. He is currently a tenured professor at the Hebrew University of Jerusalem and co-director of the Princeton Research Initiative on Climate Change and History (CCHRI). He said: “This document is part of a series of publications in recent years that cast doubt on the traditional interpretation of the plague using new methodologies. It is an exciting time to do this type of interdisciplinary research!”

Using an approach called global sensitivity analysis, White and Mordechai were able to explore the importance of any given model parameter to dictate simulated disease outcomes. They found that several poorly studied parameters are also very important in determining the model’s results. White explained, “An example was the rate of flea transmission to humans. Although the analysis described this as an important parameter, there has not been enough research to validate a plausible range for that parameter.”

These highly important variables with minimal information also point to future directions for empirical data collection. “Working with mathematical models of the disease was an insightful process for me as a historian,” Mordechai reflected. “It allowed us to examine traditional historical arguments with a new and powerful lens.”

Along with other recent work by Mordechai, this study is yet another call to examine the primary sources and narratives surrounding the Justinian plague more critically.