The Invisible Killer

In 1347, a sickness reached Europe that would kill between 30% and 60% of everyone living there within a few years. Whole villages emptied. Cities lost half their people in months. In some places, grain rotted in the fields because no one was left to bring in the harvest.

Nobody knew what germs were. People could see the disease spreading, yet had no way to explain it. Their best guesses — poisoned air, divine punishment, the stars — did nothing to slow it. The real cause would stay hidden for over 500 years.