The Black Death: How the Plague Changed Medieval Europe
The Black Death killed an estimated third to half of Europe between 1347 and 1351. Learn its cause, how it spread, and how it reshaped society and medicine.
The Black Death was a pandemic of plague that swept across Eurasia and North Africa in the middle of the fourteenth century and killed an estimated 30 to 50 percent of Europe's population in just a few years. It was caused by the bacterium Yersinia pestis, spread by fleas, and it reached Europe in 1347 and had crossed the continent by 1351, with further waves returning for centuries. It remains one of the deadliest events in recorded history and one of the most studied turning points of the medieval world.
Where did the Black Death come from?
Ancient DNA shows that the bacterium behind the Black Death descended from strains circulating in Central Asia, and the pandemic is usually traced to the steppes in the 1330s and 1340s. It travelled west along trade routes such as the Silk Road and reached Caffa, a Genoese trading port on the Crimean coast, in 1346. A contemporary account by Gabriele de' Mussi claims that besieging Mongol forces catapulted plague corpses over the city walls, a story that is probably exaggerated but reflects how quickly the disease spread.
From Crimea, Genoese galleys carried the plague to Messina in Sicily in October 1347, and from there it reached ports around the Mediterranean. It arrived in southern France and Italy in 1348, England in the summer of 1348, Germany and Scandinavia in 1349 and 1350, and Russia between 1351 and 1353. Europe had already been weakened by the Great Famine of 1315 to 1317, as the climate cooled (see the Little Ice Age).
What caused the plague, and how did it spread?
Yersinia pestis lives in fleas, which feed on rodents and also bite people. The disease takes three main forms. Bubonic plague causes swollen, painful lymph nodes called buboes, and killed roughly a third to a half of untreated patients. Septicaemic plague spreads through the blood. Pneumonic plague infects the lungs and passes between people through coughing, and it is almost always fatal without treatment.
The classic account blames fleas on black rats, but a 2018 study argued that human fleas and body lice could better explain how fast the disease crossed medieval cities. The bacterium was not identified until 1894, when Alexandre Yersin found it in Hong Kong. In 2011 researchers recovered Y. pestis DNA from skeletons in a London plague cemetery, settling an old debate about whether the Black Death was truly plague.
How many people died?
Estimates for Europe run between 25 and 50 million deaths, or 30 to 50 percent of the population. In many towns half or more of the people died, and some villages were abandoned entirely. Estimates for the whole of Eurasia and North Africa run to many tens of millions. Europe's population took about 150 years to return to its earlier level.
How did people respond?
Physicians of the time blamed corrupted air, known as miasma, and recommended fires, herbs, and flight from affected places. They had no knowledge of germs. The beaked doctor costume often shown in pictures is a later invention of the seventeenth century, not a medieval one. Some responses did work: in 1377 the port of Ragusa, now Dubrovnik, ordered arriving ships to wait thirty days before landing, and Venice later extended this to forty days, the origin of the word quarantine.
Fear also turned into persecution. Jewish communities were falsely accused of poisoning wells and were massacred in dozens of towns, including Strasbourg in February 1349, even though Pope Clement VI condemned the accusations. Groups of flagellants walked from town to town whipping themselves in penance.
What changed afterwards?
With so many workers dead, those who survived were suddenly scarce. Wages rose, tenants could bargain for better terms, and serfdom weakened across much of Western Europe. In England, Parliament passed the Statute of Labourers in 1351 in an attempt to freeze wages, which fed resentment that boiled over in the Peasants' Revolt of 1381. Land that had grown grain was often turned to sheep pasture, which needed fewer hands.
Biology changed as well. A 2022 study of ancient DNA from London and Denmark found that people carrying a particular variant of the gene ERAP2 were more likely to survive the Black Death, a vivid example of natural selection acting on a human population within a few years.
Is the plague gone?
No. Plague still occurs, with typically a few hundred to two thousand cases reported worldwide each year, mostly in Madagascar, the Democratic Republic of the Congo, and Peru. Unlike in the fourteenth century it is treatable with antibiotics such as streptomycin, gentamicin, and doxycycline if caught early, although a rare multidrug-resistant strain found in Madagascar in 1995 is a reminder of the importance of antibiotic resistance. The Black Death was part of a longer story: the Plague of Justinian struck in 541 to 549 and a third pandemic began in China in the 1850s.
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epidemiology medieval history pandemics plague public health