In the case of the latter plague, we know the offending pathogen. In a blitz of research over the past decade, three teams of scientists have positively and independently identified DNA from Yersinia pestis—the same bacterium responsible for the Black Death—in skeletons known to date from the time of the Justinianic plague.

Ancient sources make the Justinianic plague sound positively apocalyptic. According to one account, the people of Constantinople—which was by that point the capital of the Eastern Roman, or Byzantine, Empire—died at such enormous rates that the emperor Justinian had to appoint a special officer in charge of coordinating the removal of corpses from the city’s streets. The unlucky appointee, whose name was Theodore, arranged to have the bodies carted across the Golden Horn to Galata, which is now an upscale Istanbul neighborhood. In a gruesomely vivid passage, eyewitness John of Ephesus describes the process.

“[Theodore] made very large pits, inside each of which 70,000 corpses were laid down. He thus appointed men there, who brought down corpses, sorted them and piled them up. They pressed them in rows on top of each other, in the same way as someone presses hay in a loft ... Men and women were trodden down, and in the little space between them the young and infants were pressed down, trodden with the feet and trampled down like spoilt grapes.”

Despite the overwhelming numbers of corpses described in this and other textual sources, no ancient mass graves have yet been found by archaeologists in Galata or, indeed, in any other neighborhood of Istanbul. In fact, no burial pits containing anywhere near 70,000 skeletons have been found anywhere in the Mediterranean, whether dating to the 6th century or to any other period. Historians have good reason to be skeptical of any numbers mentioned in ancient texts, but there’s no doubt that the Justinianic plague claimed enormous numbers of victims across the Mediterranean. Where have all the corpses gone?

As McCormick points out, the incompleteness of archaeological excavations—and especially those in major cities, where obtaining permits and digging around modern infrastructure presents serious challenges—must contribute to the lack of known Justinianic “plague pits.” In fact, the one major Roman city of the 6th century that has been thoroughly excavated, Jerusalem, has been found to contain several mass graves, three of which held over a hundred individual skeletons.

But even if such pits could be found, they wouldn’t account for the full scale of the Justinianic Plague. While cities tend to dominate the historical record due to their concentration of the rich and powerful, the ancient world was overwhelmingly agrarian.

Influenced by the archaeology of the Black Death in London, generations of archaeologists have assumed that mass mortality events go hand in hand with large, communal burials. A close examination of the textual sources reveals, however, that even in London plague pits were not employed until the city’s usual burial places were exhausted. It follows, then, that smaller settlements in the countryside may never have faced the same burial crises as large cities: The combination of more open space and fewer people would have meant that the majority of the population may never have had to change its burial practices.