You wake up to disturbing sounds coming from outside. You lift your window to peer into the darkness. A large crowd of people is milling around in the street in front of your house. Some people are shouting. Others are crying. What's going on?

You dress quickly and sneak out the front door. People are dragging sick loved ones through the streets, desperately searching for help. Others cradle the bodies of dead loved ones in their arms. Dire warnings reach your ears. The shouts of strangers urge you to get back inside before you fall ill.

Is this the opening scene of the latest apocalyptic television series? Could such a horrible catastrophe actually happen one day? Could a large swath of humanity be wiped out by a deadly virus overnight?

Unfortunately, this isn't some pretend story on television. Instead, it's the very real disaster that struck the world in the mid-14th century. What horrible name did this tragedy go by? Historians called it the Black Death.

As early as the 1340s, Europeans began to hear rumors of a "Great Pestilence" that was killing scores of people along popular trade routes in China, India, Persia, and Egypt. Then, in October 1347, the Black Death hit Europe when trading ships traveling from the Black Sea docked in Italy.

Most of the sailors aboard the ships were already dead. The few still alive were seriously ill: feverish, overcome by pain, and covered by black boils that oozed blood and pus. Although the ships were quickly turned away, the damage was done.

The Black Death — what scientists would later call the bubonic plague — was quickly spread through the air. It was transmitted from one person to another by a bacillus called Yersina pestis. In fact, it was so contagious that merely touching the clothes of an infected person was often enough to contract the disease.

In addition to fever and painful boils, the plague also caused vomiting, diarrhea, and horrible pains. The deadly bacillus also worked quickly. People could go to bed feeling fine and still be dead by morning.

In addition to being transmitted through the air, the plague was also often spread via the bites of infected fleas and rats. Unfortunately, medieval Europe had no shortage of both these pests. Fleas and rats also loved traveling on ships, and the Black Death soon made its way all over Europe from one port city to another.

With the science of medicine in its infancy, people did not understand how the disease was transmitted or how to treat it. Plague doctors wore special masks with a beak-like nose filled with perfumes or aromatics. They mistakenly believed that the disease was transmitted via poisonous vapors with a bad smell that could be counteracted with good smells.

It took several years for the Black Death to run its course. By the early 1350s, the disease had killed over 20 million people in Europe, which was about one-third of the population at that time.

For the next several hundred years, the plague would reappear every few generations. As medicine and sanitation practices improved, however, the impact of the plague has largely been mitigated in modern times. It has not been completely eliminated, though, and remains a danger in some developing countries even today.

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