In the mid-1300s, there was an outbreak of plague so virulent that it killed between 75 and 200 million people in Asia and Europe. That is a staggering number of people for that time period, especially considering that the populations of Asia and Europe consisted of the majority of Earth’s population at the time. If the numbers we found are true, the total population of Earth in 1300 was between 300 and 500 million people. Killing off 200 million of those, if the top-end estimates are correct, make the Black Death the worst disaster in human history by far (percentage-wise at least).

Over the centuries there have been numerous attempts at trying to figure out what caused the Black Death. The prevailing idea is that the disease was carried by rats, and passed to humans through fleas. Bubonic Plague is known to travel in that manner.

Over the last few decades, however, that idea has been debated hotly, and other ideas have been proposed. The main idea that contradicts the idea that the plague was born through rats is that it wasn’t bubonic plague at all, but was instead pneumonic in nature, enabling the disease to pass from human to human.

Through archeology, we know that the disease originated in Asia, and moved along the Silk Road (one of the busiest trading routes of the day) towards the west. According to several estimates, the East was hit with much higher mortality rates due to the disease than the countries to the west. According to historian Philip Daileader, who specializes in medieval history:

“The trend of recent research is pointing to a figure more like 45–50% of the European population dying during a four-year period. There is a fair amount of geographic variation. In Mediterranean Europe, areas such as Italy, the south of France and Spain, where plague ran for about four years consecutively, it was probably closer to 75–80% of the population. In Germany and England … it was probably closer to 20%.”

Other historians suggest that the mortality rates were higher to 60 percent in the West and even higher in the East. The bottom line is that this was a major disaster that remains shrouded in mystery to this very day. With the virulence of the disease and the lack of proper medical care, hope was in short supply in Eurasia for the years between 1346-53.

From a cultural perspective, the disease was often seen as a punishment by God, who was punishing humanity for its sins. Other religious people blamed the Jewish people because of pogroms that erupted throughout Europe during those times. Pope Clement VI, the pope at the time, had to release two papal bulls in 1348 condemning people who blamed the Jews for the plague, saying that they had been “seduced by that liar, the Devil.” He, showing a lot of common sense, wrote: “It cannot be true that the Jews, by such a heinous crime, are the cause or occasion of the plague, because through many parts of the world the same plague, by the hidden judgment of God, has afflicted and afflicts the Jews themselves and many other races who have never lived alongside them.”