The Black Death is widely believed to have been plague, caused by infection with the bacterium Yersinia pestis, possibly spread by rodents infested with disease-carrying fleas. The most commonly noted symptom was the appearance of buboes (swelling of the lymph nodes) in the groin, the neck and armpits — hence, “bubonic” plague. The buboes were red at first, but later turned a dark purple or black, which oozed pus and thick, black, vile-smelling blood when lanced.