In 536, a mysterious veil of dust darkened the sky for months. The people of that time saw it as a grim omen. Shortly afterwards, a disease broke out in Egypt that would ravage the entire Mediterranean region within a few years: the Justinian Plague – one of the most devastating epidemics in history.

Over the past 15 years, researchers have succeeded in detecting the DNA of the pathogen in the skeletons of victims in Central and Western Europe. However, it remains unclear where exactly the epidemic originated and how it spread to Egypt and then on to Europe, Western Asia and North Africa.

Origins of the Justinian Plague reconstructed

An international research team from the USA, Europe and China, coordinated by historian Johannes Preiser-Kapeller from the Institute for Medieval Research at the Austrian Academy of Sciences (OeAW), has re-examined this first pandemic.

For the first time, the researchers, including numismatist Nikolaus Schindel from the Austrian Archaeological Institute of the OeAW, systematically evaluated all known historical sources from the Mediterranean region to East Asia – and combined them with the latest archaeogenetic analyses and climate history data. The results of this interdisciplinary work have now been published in the journal Nature Human Ecology as part of a collection of studies on this topic.

‘Today we know that a massive volcanic eruption – together with another eruption in 540 and a reduction in solar activity – marked the beginning of a significantly colder and more unstable climate period: the “Late Antique Little Ice Age”,’ says OeAW historian Johannes Preiser-Kapeller. These climatic changes favoured the spread of pathogens from animals to humans.

Unstable climate and global trade favoured pandemic

It has long been suspected that the pathogens responsible for the first plague pandemic – similar to the medieval ‘Black Death’ – originated in Central Asia, where the bacterium Yersinia pestis is still found in wild animals today. The discovery of ancient plague DNA from around 200 AD near the Tian Shan Mountains in Kyrgyzstan seemed to confirm this. However, the new analysis shows that this variant is genetically further removed from the pathogens of the 6th century than originally thought.

Either variants of the pathogen reached India via trade routes from Central Asia shortly before the first documented outbreak in Egypt in 541, and from there by ship to the land on the Nile – or it was introduced to East Africa centuries earlier and developed there into the strains that later proved so devastating. ‘Our investigation shows that both routes are plausible given the historical and ecological conditions,’ explains Johannes Preiser-Kapeller.

Global perspective

Chinese texts were also evaluated for the first time in the study. These report cases of disease with the typical buboes of the plague in the 5th and 6th centuries – described as ‘evil kernels under the skin’. However, pandemics on the scale of the Mediterranean catastrophe are not documented there, possibly because the East Asian strains were less easily transmitted from person to person.

Future DNA findings could be crucial in clarifying the exact origin and spread of the Justinian plague. ‘The results are a solid starting point for further research – and show how complex and globally interconnected pandemics were even in ancient times,’ says Preiser-Kapeller.