The Black Death killed up to half of Europe

When plague reached Europe in 1347, it spread with terrifying speed. By 1351 it had swept from Mediterranean ports to the far north, leaving an estimated 25 million dead in its wake.

The killer was the bacterium Yersinia pestis, carried by fleas riding on black rats. The bubonic form announced itself with the swellings that gave the disease its later name: painful, egg-sized buboes in the groin and armpits, often followed by blackened skin as blood vessels hemorrhaged beneath it. Worse still was the pneumonic form, which settled in the lungs and spread person to person through the air — no rat or flea required. It moved faster and was very nearly always fatal.

For decades the standard figure held that roughly a third of Europeans perished. Newer research has pushed that grimmer: studies of manorial and tenancy records suggest the true toll was closer to 50%. In England, the population is thought to have fallen from about 4.8 million in 1348 to 2.6 million by 1351.

The population of western Europe did not climb back to its pre-plague level until around the start of the 16th century.

The social wound ran as deep as the demographic one. Bands of flagellants whipped themselves through towns to beg God’s mercy, while frightened communities looked for scapegoats — leading to the massacre of Jewish communities falsely accused of poisoning wells. With workers suddenly scarce, surviving laborers could demand higher wages, loosening the bonds of serfdom and feeding later revolts, including England’s 1381 Peasants’ Revolt.