Terrifying Illness. When violent and relatively abrupt sickness and death struck seemingly healthy individuals without warning and began to sweep across Europe in 1347-1348, these occurrences shocked and baffled members of every class of society. Medical lore had preserved distant memories of plague in Athens in 430-427 B.C.E., and scattered historical chronicles noted plagues that had eroded the economy and military might of late Imperial Rome in the sixth century C.E. By the late Middle Ages these events were, for the most part, forgotten. No one in medieval Europe had experienced anything like the epidemic death that arrived in Italy on board ships from the East, ravaged almost all of Europe, and recurred every ten to twenty years, terrifying people and hindering population recovery, until it disappeared without explanation in the early eighteenth century.

Case Fatality. Symptoms of...