Historic Pandemics and Their Global Spread

The Plague of Justinian, which struck the Byzantine Empire beginning in 541 CE under the reign of Emperor Justinian I, is the earliest pandemic for which reasonably detailed written accounts survive, chiefly through the contemporary historian Procopius, who described it striking Constantinople in 542 CE and, at its height, killing an estimated 5,000 people a day in the capital. Genomic analysis of ancient DNA recovered from burial sites, published by researchers including Michael McCormick and David Wagner in the 2010s, confirmed the causative agent as Yersinia pestis, the same bacterium responsible for the later Black Death, and traced its likely origin to Central Asia, from where it moved along Byzantine trade and grain-supply routes linking Egypt to Constantinople. The pandemic recurred in waves for roughly two centuries, and historians such as McCormick have argued it contributed to weakening the Byzantine and Sasanian empires on the eve of the 7th-century Arab conquests, though the scale of its long-term demographic and political impact remains a matter of active historical debate.