New World Smallpox: 25–56 million (1520–early 1600s)
Smallpox had been a famous scourge in many parts of the world for centuries in a row, but it all started when the first Europeans arrived on American shores. 60% of infected people died.
The survivors emerged immune. However, the pre-Columbian indigenous people in America were immunologically compromised by the variola virus that landed aboard a Spanish ship in present-day Veracruz, Mexico, back in April 1520.
The ship was hiding the body of an infected, enslaved African man. The continent was extremely vulnerable. The outbreak seeded by first contact was, as you can imagine, catastrophic, but it was only the first round.
Waves of infection broke out on the continent for many decades. In fact, anyone who didn’t die of smallpox was then killed by the imported influenza that followed the smallpox or measles epidemic.
A mind-blowing 90 percent of the indigenous population died. What’s even worse is that great civilizations and their cultures perished altogether, clearing the path for European colonization.
Plague of Justinian: 30–50 million people (541–549)
The disease, which is now known as the bubonic plague, arrived in Constantinople, the capital of the Late Roman or Byzantine Empire, in 541 AD. Soon enough, it killed 10,000 people a day.
Corpses littered public spaces and were kept like produce indoors. It was the first big outbreak of bubonic plague the world has ever seen, and the records show that it extended across many continents, reaching Roman Egypt, the Mediterranean, Northern Europe, and even the Arabian Peninsula.
Recent scholarship analyzing scientific findings with textual records points to the possibility that it might have left an even bigger imprint on the early medieval world than it was previously acknowledged.
