1. The Antonine Plague
The cause of this ancient pandemic is still a mystery but it was thought to be likely caused by either Smallpox or Measles. The Antonine Plague, otherwise known as the Plague of Galen, swept through Asia Minor, Egypt, Greece, and Italy.
It is believed that this unknown disease arrived around 165AD, likely brought to Rome but soldiers returning from a campaign in Mesopotamia. It would eventually decimate the Roman army and be the cause of an estimated 5 million deaths.
2. The Plague of Justinian
This is believed to be the first recorded incident of the bubonic plague and one that killed half the population of Europe. In the space of just one year, the Plague of Justinian was thought to have claimed the lives of up to 25 millions people in the Byzantine Empire and Mediterranean port cities between 541AD and 542AD.
It got so bad that at one point the plague was estimated that in the city of Constantinople to be killing 5,000 people per day, resulting in the deaths of 40% of the city’s population.