The Black Death was a devastating pandemic that swept through Europe in the 14th century. It was caused by the bacterium Yersinia pestis, which was carried by fleas on rodents and spread to humans. The disease had three forms: bubonic plague, pneumonic plague, and septicemic plague. Symptoms varied but included swollen and painful lymph nodes, coughing, and bleeding from orifices. Treatment options were limited and mortality rates for each form were extremely high. The plague drastically reduced Europe's population and permanently changed societal structures and practices.