The Black Death
The Black Death or Plague was one of the worst pandemics in human history. Beginning in central Asia it spread to Europe by the late 1340's. It is estimated that 75 million were killed and of these 20 million were in Europe. When it began it was called the Great Mortality.
The first reports of the plague come from China around 1330 AD. In 1347 AD a fleet of Genovese trading ships fleeing the besieged port of Caffa in the Crimea landed in Medina, Italy. All the crew were either infected or dead. From Italy the plague spread quickly, France, Spain, Portugal and England were infected by June 1348 AD. From there it went to Germany, Scandinavia and Russia. Fortunately there were enclaves where it never gained a foothold. These included Poland and parts of Belgium and the Netherlands.
England lost up to 70% of its population, down from 7 million to 2 million in 1400 AD. The plague didn't completely die out; it continued to recur through to the 17th century with the Great Plague of London (1665 AD/1666 AD) being one of the last outbreaks.
There were three main types of plague:
3. The 100% fatal but less common Septicaemic plague
As to the cause of the plague, there are many theories but no definitive answer. It was long believed that fleas carried by rats brought the plague but other arguments advanced include:
1. Pulmonary anthrax
2. An Ebola type virus as opposed to a bacteria
How quickly did it spread? Around 5 kms a day, which, when you think about how sparsely populated Europe was at that time, is truly amazing.