In the mid-14th century a pandemic spread along trade routes from Central Asia into the Near East, North Africa, and Europe. Within the few years between 1347 and 1351, an estimated one third to one half of Europe's population is thought to have died; the proportions vary greatly by region and the figures are approximate. The pathogen is today attributed to a bacterium, though the details of the transmission mechanism are still debated.

Its scale made it more than a health event. The sudden contraction of the labor force changed wages and land relations; in some regions peasants' bargaining power rose and established orders were shaken. The pandemic also escalated social tension: the scapegoating of minorities and violence were among the dark consequences of the crisis. Religious, artistic, and medical thought long remained under the shadow of this experience.

The Black Death is among the clearest examples of how a biological event can produce a historical rupture: no army or ruler, but an invisible agent, reshaped social structure on a continental scale.