The exact nature of the disease that killed so many millions of Europeans in the outbreak from 1347 on, and in many subsequent outbreaks, is the subject of intense debate, by historians and microbiologists alike.

Conventional wisdom identifies the Black Death as being the disease known to modern medicine as bubonic plague, caused by the microorganism Yersinia pestis.

Some researchers, however, have noted that the medieval descriptions of the Black Death make a poor match with what is known today of bubonic plague. They would argue that the historical epidemic we know as the Black Death was actually caused by anthrax, or possibly smallpox.

My personal conviction is that the "Black Death" was probably several infectious diseases, lumped together - but that the bubonic plague (caused by Yersinia pestis) was the most significant one.

However, for the purposes of this project, the actual agent of the Black Death is irrelevant - as irrelevant as it would have been to the people dying of it in the 14th century. What matters is the geographic spread and impact of the disease - which is what I have attempted to show, in a graphic (and hopefully illustrative) fashion.

For more information on the Black Death, I refer you to my general page on the subject.