If one wants to imagine the ultimate worst-case scenario for the ongoing global coronavirus pandemic, there’s no need to look further than the Black Death, a global epidemic of bubonic plague that struck Europe, Asia and North Africa in the mid-1300s.

The Black Death—also known as the Pestilence, the Great Mortality, and the plague—is considered the deadliest pandemic in human history, as it resulted in the deaths of an estimated 75 to 200 million people.

For comparison, now roughly eight months into the current coronavirus pandemic, there have been at least 814,000 deaths, according to the latest data from Johns Hopkins University.

The 1918 flu outbreak, however, matches up much better in terms of the overall death toll of the Black Death. Lasting from February 1918 to April 1920, the contagion infected a third of the world’s population in four successive waves and killed at least fifty million people—roughly 675,000 of them in the United States, according to the Centers for Disease Control and Prevention.

What made the Black Death so devastating was the fact that it occurred in the fourteenth century. The people at the time did not have access to modern improvements in hygiene, viable vaccines and antibiotics, and time-tested guidelines for public health and safety.

Therefore, when the plague arrived in Europe in October 1347, when twelve ships from the Black Sea docked at the Sicilian port of Messina, doctors and the public weren’t equipped to deal with the terrible reality of the disease.

“In men and women alike,” the Italian poet Giovanni Boccaccio wrote, “at the beginning of the malady, certain swellings, either on the groin or under the armpits … waxed to the bigness of a common apple, others to the size of an egg, some more and some less, and these the vulgar named plague-boils.”

Today, the plague can be treated with antibiotics, but at that time, no one had the knowledge or resources to combat the swellings, fever, chills, vomiting, diarrhea, and aches and pains.

How the disease was transmitted was a mystery as well. One doctor said at the time: “Instantaneous death occurs when the aerial spirit escaping from the eyes of the sick man strikes the healthy person standing near and looking at the sick.”

Now, medical experts know that the plague, caused by the zoonotic bacteria Yersinia pestis, travels from person to person through the air, as well as through the bites of infected fleas and small mammals. The disease also specifically targets the lymphatic system, which causes swelling in the lymph nodes. If left untreated, the infection can spread to the blood or lungs.

Eventually, through strict quarantine measures and social distancing, the plague’s rate of spread was slowed to a point where it became manageable. But even today, the disease hasn’t been totally eradicated. According to the World Health Organization, there are between 1,000 and 3,000 cases of the plague each year.

Ethen Kim Lieser is a Minneapolis-based Science and Tech Editor who has held posts at Google, The Korea Herald, Lincoln Journal Star, AsianWeek and Arirang TV. Follow or contact him on LinkedIn.