The Black Plague, also known as the Black Death, was a bubonic plague pandemic that primarily occurred in Europe from 1346 to 1353. It was one of the most fatal pandemics in human history, killing an estimated 25 to 50 million people, which was about half of Europe's population at the time. The plague is caused by the bacterium Yersinia pestis and was spread by fleas on rats and also via airborne transmission in its pneumonic form. The pandemic started spreading to Europe through trade routes and reached significant ports and countries like Italy, France, England, and others in that period.