In the 14th Century, the epidemic Black Plague has ravaged in Europe. It has killed nearly one-third of Europe's population at that time.
It was caused due to the bacterium - Yersinia pestis which is transmitted to humans from infected rats and caused plague. This was confirmed in the recent DNA tests on 600-year-old teeth from victims of the Black Death that they had black plague caused by Yersinia pestis.
The victims of this plague had to bleed below their skin due to subcutaneous hemorrhage, which darkened/blackened their bodies. People used to get gangrene of the fingers, toes, and nose. The entire body used to become black. Death due to this Plague is termed as Black Death.