The Great Plague, also known as the Black Death, occurred in Europe from 1347 to 1351. It was caused by the bacterium Yersinia pestis, which was transmitted through fleas that lived on rats. The disease spread rapidly, leading to the deaths of an estimated 25 million people, about one-third of Europe's population at the time. The Great Plague had significant social and economic impacts. Many towns and villages were abandoned due to fear of the disease, leading to labor shortages. This shift contributed to changes in the feudal system, as surviving workers demanded higher wages and better working conditions, ultimately altering the course of European history.