Today, we know that there were many causes of the Black Death:
Causes of the Black Death
Medieval European medicine was very different from our modern concept of medicine. There was no knowledge of germs, and only relatively basic tools to diagnose and treat illness. Much of medicine was, at best, based on ancient Roman and Greek ideas of the 'humours'. The ideal was to balance specific fluids known as 'black bile', 'yellow bile', blood and phlegm (the fluids made by your ear, nose and throat). To be in a bad or good humour was evidence of how healthy you were! Other doctors would release "evil spirits" by trepanning (drilling a hole in your head to release them). In this context it is not surprising that the causes listed below emerged.
Medieval doctors were not certain what caused the plague, but believed it could be the result of:
We would consider Medieval society as superstitious. Think about the ideas above: