But not everyone was on board with Olson’s theory. In a 1996 interview with the The New York Times, the epidemiologist David Morens argued that Thucydides wasn’t the most reliable source: Unlike his contemporary, Hippocrates, he wasn’t a physician, and many of the terms he used to describe the disease’s symptoms were ambiguous. For example, the ancient Greek phlyktainai could refer to either blisters or callouses. Noting Thucydides’ claim that the epidemic had originated “in the parts of Ethiopia above Egypt” (today’s sub-Saharan Africa), Morens also questioned how people with Ebola, a highly contagious and deadly disease, could make it all the way to Greece without dying along the way.

The duration of the Athens epidemic also presented another problem: At five years, it was much longer than any known Ebola outbreaks, the majority of which lasted less than a year. And finally, Morens asked, if Ebola had made it out of Africa millennia ago, why were there no other accounts of the disease re-appearing anywhere on Earth until 1976?

Unfortunately for both Olson and Morens, however, neither had a more concrete way to back up their arguments. Their efforts to identify the Plague of Athens, like all the other efforts before them, could only rely on the written record left by Thucydides, which made confirmation more or less impossible.

This, in a nutshell, is the challenge of ancient pathology: With DNA testing, it’s often possible to identify the cause of an epidemic that took place centuries or even millennia ago. Finding remains of those victims to test, though, is another story.

Sometimes, scientists get lucky. In 2001, for example, a mass grave was uncovered at a construction site in Vilnus, Lithuania. Based on uniform fragments found in the grave, the bodies were identified as belonging to soldiers in Napoleon’s army—somewhere between 2,000 and 3,000 of them, hurriedly buried during the retreat from Moscow. When a team of anthropologists examined dental pulp taken from the bodies, they found that around one-third of them had died of typhus, a finding confirmed by tests of dead lice found at the site (the disease is transmitted through lice). Researchers had long suspected that typhus had contributed to Napoleon’s eventual defeat, but because knowledge of the disease was scant during his lifetime, historical accounts alone had never been enough to confirm it.

For the Plague of Athens, it seemed like a similar turning point had arrived in 1994, when during excavations for a planned Athens metro station at Kerameikos, an ancient graveyard used from the early Bronze age through Roman times. The excavators uncovered thousands of previously undiscovered tombs—including a set of seemingly hurried, unceremonious mass burials dating to 430 B.C., the year of the Plague of Athens.