Answer: The Plague of Justinian
Long before the black plague swept through Europe and decimated the population in the 1
When people began to gather in large numbers in early city-states, pests came with them to hunt and refuse their food supplies. Along with that pests came fleas (the real carriers of the bacteria); that vermin in combination with the bad sanitary practices of the day led to frequent and devastating outbreaks of the bacteria. Long before the astonishing number of deaths around the 1340s and 1350s in Europe, there was a smaller, but still deadly, outbreak around the 6th century known as the scourge of Justinian caused by the bacteria that calmly and with great consequences around Asia would travel and Europe for centuries.
Despite Yersinia pestis infections with high mortality rates ranging from 80 to almost 100 percent in untreated cases, depending on the contracted variety (bumps, pneumonia or septicemia), Justinian the I (the Roman emperor at the time of the original outbreak) survived a brush with the plague that would later be named after him.