Killed close to 25,000,000 people.
The Black Plague started in China or central Asia, before spreading west. The plague then travelled along the Silk Road all the way to the Black Sea. From there, it was most likely carried by fleas living on the rats that were regular passengers on merchant ships. Spreading throughout the Mediterranean and Europe, the Black Plague is estimated to have killed 30–60 percent of Europe's population. Reducing the worlds population to from an estimated 450 million to 350 and 375 million in the 14th century.