Outbreaks of Y. Pestis have plagued human history for millennia. The first recorded outbreak of a similar plague occurred 541 A.D. in the Byzantine Empire. It was named the Justinian plague after the emperor of the time. However, the largest and most well-known outbreak was the European Black Death, which occurred approximately 1349-1356. It killed roughly one-third of Europe’s population and millions more throughout the world. Additionally, a much more recent outbreak in 19th century China led to the loss of more than of 25 million people. Plague has caused human suffering for thousands of years and is clearly a very devastating disease.