Between 1347 and 1351 a great epidemic known as the Black Death (Black Plaque or Bubonic Plague) ravaged Europe. This pandemic took a proportionately greater toll of life than any other known epidemic or war up to that time. The Black Death is widely believed to have been the result of plague that was caused by infection with the bacterium Yersinia pestis. Most scientists think that this bacterium was first passed from infected rodents to humans through the bite of fleas. Then it spread quickly from one person to another.