750-Year-Old Forgotten Plague Outbreaks: New Study Challenges Timeline of the Black Death’s Arrival

New research suggests that plague was present in the Middle East nearly a century before the Black Death.

A new study suggests that plague may have played a role in epidemics as early as the 13th century—nearly a century before the Black Death—based on evidence from contemporary chroniclers and physicians.

The bacterium Yersinia pestis, responsible for the plague, likely reached the Middle East around 100 years before the devastating outbreak of 1346–1351.

While some experts have argued that Y. pestis only became established in western Eurasia after the Black Death, this study indicates that the bacterium may have quietly circulated in local insect and rodent populations long before. Environmental and climatic pressures may have eventually triggered the widespread human outbreaks that marked the Black Death’s onset.

The new study, by historians of medicine Dr Monica H. Green, an independent scholar, and Professor Nahyan Fancy, from the University of Exeter, builds on earlier work that documented the likely role of plague in a series of epidemics in western Asia in the late 1250s. The researchers used over a dozen pre-1348 chronicles, religious, and medical texts from the region.

Recognizing Plague in Historical Records

In a previous study, they showed how multiple contemporary observers were suggesting the new presence of a plague-like disease in western Asia in the second half of the thirteenth century, nearly a century before historians have hitherto assumed it arrived.

In this new study, they show how close examination of the symptoms described suggested that this was indeed the disease now known to be caused by the bacterium Yersinia pestis, whose evolutionary history is in the process of being newly outlined by geneticists. Some writers even used the specific Arabic term for plague, which has the distinctive characteristic of causing inflamed and tender swellings of the lymph nodes known as “buboes”.

Professor Fancy said: “In the thirteenth century, of course, there were no microscopes and no means to conceive of bacteria as the cause of disease. Rather, contemporary observers believed that epidemics were caused by “miasms,” airborne effluvia that could arise from scenes of decay, like the sites of great battles. Observers linked outbreaks of plague in Syria, Iraq, and Egypt up through 1260 to the Mongol conquest of Baghdad in 1258, where epidemic disease was reported even among the Mongol troops.”

Plague’s Early Spread and Its Long-Term Impact

The new study gives further evidence for the arrival of plague in Western Iran, Iraq, and Egypt in the 1250s, but also a framework for how medical historians can fruitfully engage with historical sources and modern genetics to reconstruct how the plague bacterium established itself in new environs for a century before the unprecedented crescendo of plague activity throughout the region and beyond in the 1340s.

Professor Fancy said: “It’s important to examine carefully how pathogenic organisms spread. Plague is primarily a rodent disease which is reported in historical (and often even contemporary) sources only when it spills over into humans. Moreover, in order to spillover, it needs vectors like fleas or lice. A prolonged and widespread human outbreak of plague, a pandemic like the Black Death, and the hundreds of years of plague waves that followed it, can only have happened after an earlier period in which the bacterium had been able to find new suitable host animal species and insect vectors. This is what we are calling the ‘prodrome’ of the pandemic, in which the bacterium is present in the region but a full-blown pandemic has not started raging yet.”

Dr Green explained: “We know now that the strains of Yersinia pestis that reached Europe in the fourteenth century are most closely related to those still found in Central Asian marmots. That core biological narrative prompts us to look for an importation mechanism. The troops’ grain supplies in the 1250s could explain that. But what happened next?

“Because humans in the Middle Ages had no concept of microbes, we will never find bacteria mentioned in our written sources. But when a scribe reports ‘pestilence’ and an infestation of fleas in his region more than 25 years before the Black Death, we need to pay attention.”

Reference: “Plague history, Mongol history, and the processes of focalisation leading up to the Black Death: a response to Brack et al.” by Monica H. Green and Nahyan Fancy, 17 February 2025, Medical History.