Some of the worst epidemics, widespread outbreaks of disease, have troubled mankind for millennia. In one of the earliest recorded epidemics, the Roman Empire lost almost a third of its population between 165 and 180 AD to Antonine Plague, a deadly virus contracted in the Middle East and brought back to the heart of the empire by returning soldiers. Characterized by fever, diarrhea and outbreaks of the skin, it is generally thought to have been a far-reaching outbreak of smallpox or measles.
There have been many other epidemics that have devastated populations and changed the course of history. The Black Death killed 75 million people worldwide in the 14th century, around 25 million of them in Europe alone, which was somewhere between 30% and 60% of the total population. We have triumphed over some deadly diseases—smallpox was the first deadly human disease to be completely eradicated from nature—but elsewhere, epidemics still unfortunately take thousands of lives daily.