Disease and demography
- The plague - named the Black Death by later historians - was caused by the yersinia pestis bacteria, which lived in rodent populations and was spread by fleas that had bitten infected animals.
- Once the plague transferred to animals that were in close contact with humans and to humans themselves, it began to spread along established trade routes.
- It is difficult to measure the exact human cost of the plague due to limited records from the historical period.
- Most historians think that the plague killed somewhere between 30% and 60% of Europe’s population between 1347 and 1351.