Y. pestis was the notorious culprit behind the sixth century's Plague of Justinian, the Black Death, which killed 30%-50% of the European population in the mid-1300s, and the Third Pandemic, which emerged in China in the 1850s. Earlier putative plagues, such as the Plague of Athens nearly 2,500 years ago and the second century's Antonine Plague, have been linked to the decline of Classical Greece and the undermining of the Roman army. However, it has been unclear whether Y. pestis could have been responsible for these early epidemics because direct molecular evidence for this bacterium has not been obtained from...