The Justinianic Plague spread through west Eurasia between the 6th and 8th centuries CE, signifying the first known outbreak of bubonic plague in this part of the world.

According to a new analysis of ancient texts and genetic data, its impact was much more severe than some recent studies have suggested.

Certain scholars think this 'first pandemic' may have killed up to half the population of the Mediterranean region at the time, helping to bring down the Roman Empire.

Meanwhile, other historians argue the consequences were far less significant, and suggest the outbreak might not have had any more impact than the flu does in modern society today.

Which brings us to this latest study. Historian Peter Sarris from the University of Cambridge says historians and archeologists need to work together with geneticists and environmental scientists to fully understand the scope and scale of ancient disease outbreaks – including, in this particular example, the arrival of the bubonic plague.

"Some historians remain deeply hostile to regarding external factors such as disease as having a major impact on the development of human society, and 'plague skepticism' has had a lot of attention in recent years," Sarris says.

Sarris points to a number of clues that show the devastating impact of the Justinianic Plague, including a flurry of crisis measure legislation passed between the years 542 and 545 CE as the population dropped, followed by a reduction in law making as the pandemic fully took hold.

A law passed in 542 designed to prop up the banking sector of the imperial economy, for example, was described as having been written amid the "encircling presence of death" by Justinian. Other laws at the time were intended to avoid the exploitation of workers during what seemed to be a severe labor shortage.

What's more, a series of lightweight gold coins were issued, representing the first reduction in the value of gold currency for centuries – something that would have been seen as emergency banking legislation at the time. The heavy weight of copper coins circulating in Constantinople was reduced at around the same time.

These signs are more significant than examples cited by other historians, Sarris argues. Some studies use the relatively infrequent mentions of the plague in ancient literature as evidence that its effects weren't all that widespread or damaging to society.

"Witnessing the plague first-hand obliged the contemporary historian Procopius to break away from his vast military narrative to write a harrowing account of the arrival of the plague in Constantinople that would leave a deep impression on subsequent generations of Byzantine readers," says Sarris.

"That is far more telling than the number of plague-related words he wrote. Different authors, writing different types of text, concentrated on different themes, and their works must be read accordingly."

Sarris also highlights the growing amount of DNA evidence showing just how far the bubonic plague spread during this time – all the way to Edix Hill in England, according to a 2018 genetic analysis of a burial site, in one case mentioned in the research.

DNA analysis like this is a much more reliable method of working out where the plague spread to, Sarris says, compared with leafing through ancient texts. It can also shed new light on the routes that the disease took around Europe as it spread.

In this particular case, the disease may have spread to England through the Baltic and Scandinavian countries, arriving there before it hit the Mediterranean – and giving historians a fresh understanding of how this 'first pandemic' evolved.

"We have a lot to learn from how our forebears responded to epidemic disease, and how pandemics impacted on social structures, the distribution of wealth, and modes of thought," says Sarris.

"Increasing genetic evidence will lead in directions we can scarcely yet anticipate, and historians need to be able to respond positively and imaginatively, rather than with a defensive shrug."

The research has been published in Past & Present.