The Black Death was one of the most devastating pandemics in human history, peaking in Europe between 1348 and 1350, and killing between 75 million and 200 million people. Although there were several competing theories as to the etiology of the Black Death, recent analysis of DNA from victims in northern and southern Europe indicates that the pathogen responsible was the Yersinia pestis bacterium probably causing several forms of plague.

The Black Death is thought to have started in China or central Asia. It then travelled along the Silk Road and reached the Crimea by 1346. From there, it was probably carried by Oriental rat fleas living on the black rats that were regular passengers on merchant ships. Spreading throughout the Mediterranean and Europe, the Black Death is estimated to have killed 30 to 60 percent of Europe's population. All in all, the plague reduced the world population from an estimated 450 million to a number between 350 and 375 million in the 14th century.

The aftermath of the plague created a series of religious, social and economic upheavals, which had profound effects on the course of European history. It took 150 years for Europe's population to recover. The plague reoccurred occasionally in Europe until the 19th century.