TheBlackDeathUp to Six in Ten Europeans Dead in Six Years

On a stone in the cemetery of Kara-Djigach, in the Chüy Valley of Kyrgyzstan, a stonecutter carved in Syriac: "This is the tomb of the believer Sanmaq. He died of pestilence." The year corresponds to 1338. In that cemetery and in the one at Burana, burials from 1338 and 1339 are abnormally numerous.

*In 2022, a team led by Maria Spyrou and Johannes Krause analyzed DNA from seven of those dead and found Yersinia pestis in three of them* — and not just any strain: the one from which the four main lineages of the modern bacterium branch out like a star. Plague was therefore born neither in southern China nor in the Indian deltas, as was long supposed: it jumped to humans in Central Asia, in a region where marmots and their parasites remain its primary reservoir to this day.

Those villages did not live in isolation. The valley traded, and the site lay within reach of the networks that crossed Asia. All it took was a rodent bacterium, merchant roads, and nine years for it to come ashore in Sicily.

The story everyone knows fits in a single image: in 1346, outside the Genoese trading post of Caffa in Crimea, the army of the Golden Horde, decimated by plague, had its own corpses loaded onto siege engines and hurled over the walls. The notary Gabriele de' Mussi relates that "what seemed like mountains of dead were thrown into the city" and that the Christians could neither hide nor flee.

The problem is that de' Mussi was not there. His account is secondhand and no other source confirms it; the microbiologist Mark Wheelis, who reexamined it, judges that the corpses probably infected the besieged, but that "it is unlikely that the attack had a decisive role in the spread of plague to Europe." Other Crimean ports were in Mongol hands, and caravans were carrying the bacillus southward. History's most famous biological weapon is above all a good story.

What is certain, whatever route it took, is its arrival in Sicily. At the beginning of October 1347, twelve Genoese galleys entered the port of Messina. The Franciscan Michele da Piazza, writing his chronicle about ten years later, said of the sailors that "in their bones they bore so virulent a disease that anyone who only spoke to them was seized by a mortal illness." From Messina, the disease moved up the Mediterranean, then up the rivers, then along the roads.

The mechanism itself has a repulsive elegance. In the flea's foregut, the bacterium builds a sticky mat that eventually plugs the passage; the starving flea bites relentlessly, and each time it sucks, the blood hits the plug and flows back into the wound, loaded with bacilli. The vector of the greatest epidemic in history was an insect kept from eating its dinner.

The rat, for its part, has dragged around a reputation for six centuries that it might well ask to have reviewed. In 2018, a Scandinavian team compared the mortality curves of nine European epidemics with three models of contagion: the model of rats and their fleas fits less well than that of human parasites, fleas and body lice, passing from one sleeper to the next. The authors do not exonerate anyone, but they challenge the idea that plague in Europe spread mainly through rats. In other words, we may have passed the scourge to one another ourselves, from bedding to bedding.

Boccaccio watched. "In men and women alike there appeared, at the beginning of the malady, certain swellings, either on the groin or under the armpits, whereof some waxed of the bigness of a common apple, others like unto an egg," he wrote; then fever, then "black or livid spots" on the arms and thighs, and death within a few days.

Three forms, a single bacillus. The bubonic form, the most common, lodges the bacterium in a lymph node that swells and suppurates; untreated, it kills between 30 and 60% of patients. The septicemic form passes directly into the bloodstream and turns the extremities black with necrosis. The pneumonic form, finally, spreads from one person to another through droplets, without flea or rodent: the WHO notes that it can kill within eighteen to twenty-four hours of the first signs. A cough in a closed room was enough to condemn a household.

It was long believed that this scourge killed indiscriminately: too virulent, too new, facing bodies without immune defenses. The skeletons say otherwise. Comparing London's East Smithfield cemetery, dug for the plague, with ordinary Danish cemeteries, Sharon DeWitte and James Wood showed that mortality remained selective: the already frail died in greater numbers. The plague killed a great many people, but it began with the hungry, the sick, and the old.

It also struck those whose calling was to approach the dying: in parts of the Archdiocese of York, mortality among the clergy reached as high as 48%. And the peasants, in the fields they plowed, "died not like men, but like beasts."

In Florence, consecrated ground ran short. In the churchyards they dug "huge trenches, wherein they laid the corpses as they arrived by hundreds at a time," wrote Boccaccio: "piled up in those trenches, like goods in the hold of a ship, layer upon layer." He described a city where "brother forsook brother, uncle nephew, and sister brother," and where "fathers and mothers refused to visit and tend their children, as if they had not been their own." He put the toll at more than a hundred thousand dead between March and July within the city walls — a figure historians consider far above reality, like most numbers left by chroniclers.

In Siena, the shoemaker Agnolo di Tura wrote down the same sentence about abandoning one's own kin, then added the one that contradicts it: he buried his five children with his own hands.

In Ireland, the Franciscan John Clyn kept his annals in Kilkenny. He explained that he was writing "among the dead, waiting for death till it come," and that he "leaves parchment for continuing the work, if haply any man survive." The copyist who transcribed his manuscript added beneath the last line: Here it seems the author died.

How many dead in all? Historians still do not agree, and the gap between them is dizzying: nearly four in ten inhabitants for some, more than six in ten for others. Most of the data comes from a few urbanized regions of Italy, England, Spain, France, and Germany; elsewhere, scholars extrapolate from three parishes. Everyone is therefore counting dead people a large share of whom were never recorded anywhere.

In 1348, Philip VI asked the Medical Faculty of Paris for an explanation. In October, forty-nine masters delivered a solemn report. The cause, they wrote, went back to 1345: "In 1345, at one hour after noon on 20 March, there was a major conjunction of three planets in Aquarius."

Risk factors followed. Those who succumb fastest are those following "a bad life style, with too much exercise, sex and bathing," as well as "corpulent people with a ruddy complexion." Those who adopt a sensible regimen, by contrast, "will succumb to the pestilence more slowly." Finally, the faculty conceded that "God alone cures the sick" and that "a sure explanation and perfect understanding of these matters is not always to be had." On that last point, it was right.

The only effective weapon of the age came not out of a university faculty, but out of a port. In 1377, Ragusa — Dubrovnik — imposed isolation on new arrivals before they could enter the city; no one knows why the duration was eventually set at forty days, which gave us the word quarantine. In 1423, Venice opened the first permanent plague hospital on the small island of Santa Maria di Nazareth. The Middle Ages understood nothing about the disease, but it understood the door.

For want of a cause, people looked for culprits. The rumor of poisoned wells traveled as fast as the bacillus, and confessions were extracted under torture: in Bern and Zofingen, the Strasbourg chronicler Jacob von Königshofen reported, tortured Jews "admitted that they had put poison into many wells."

On February 14, 1349, in Strasbourg, about two thousand Jews were burned on a wooden platform erected in their cemetery. "Many small children were taken out of the fire and baptized against the will of their fathers and mothers." Debts owed to them were canceled and their money divided up. The chronicler, who was no defender of theirs, wrote the coldest sentence in the entire record: "The money was indeed the thing that killed the Jews."

The plague itself did not enter Strasbourg until the following summer, when the dead were estimated at sixteen thousand. Pope Clement VI had, as early as 1348, addressed a bull to the prelates asking them to protect the Jews against the accusation of having brought on the plague, calling their accusers people seduced by the Devil. The Jewish communities of Basel, Mainz, Worms, Frankfurt, and Erfurt were destroyed or massacred despite it.

The third response did not look for a culprit: it struck itself. In the spring of 1349, bands of flagellants began their penitential processions in southern Germany; that same year, they reached Flanders, Holland, Bohemia, Poland, and Denmark, then England in September, where they met with little success. Many towns shut their gates upon them.

The papacy first encouraged public penance, then banned it. In 1348, Clement VI had himself authorized a similar procession in Avignon to ward off the plague. On October 20, 1349, at the request of the University of Paris, he condemned the movement in letters sent to the bishops of France, Germany, Poland, Sweden, and England, and prohibited the processions. Many flagellants ended up at the stake or in the cells of the inquisitors.

Before 1347, Western Europe was too full: poor land brought under the plow, stagnating yields, hands in surplus and therefore worthless. By removing one in three inhabitants, or even one in two, the plague reversed the balance of power between land and labor. In England, farm wages doubled on average between 1350 and 1450. Yet the effect was not immediate: in the first years, inflation swallowed the increases, and real wages initially fell.

Edward III tried to stop this by law. The Ordinance of Labourers of 1349, followed by the Statute of Labourers of 1351, decreed that no peasant could ask for more than in 1346, on pain of paying back double what had been given — triple for lords who outbid one another. A king of England was legislating against supply and demand; it would not be the last time, and the result would always be the same. The resentment accumulated against those laws fed the Peasants' Revolt of 1381.

Serfdom disappeared from Western Europe, while in Eastern Europe harsher laws instead bound peasants to the land: the same catastrophe freed one side of the continent and chained the other. On the tables of those who remained, meat and dairy products took the place of grain porridges. Florence, which had between 110,000 and 120,000 inhabitants in 1338, had 50,000 in 1351. Europe did not regain its fourteenth-century level until the sixteenth.

That delay had a simple cause: the plague came back. In 1361-1362, a "second plague" struck England and Wales; the historian Philip Slavin showed in 2024 that it had been harsher than supposed, with heavy and lasting demographic consequences. Return waves followed one another for centuries, down to the Great Plague of London of 1665-1666, which may have killed about 100,000 Londoners, and the outbreak that struck Marseille in 1720, the last great plague of Western Europe.

The Black Death was not a six-year catastrophe, but the first wave of a disease that did not leave the West until the eighteenth century.

Unlike smallpox, Yersinia pestis has never been eradicated: it still lives in wild rodents across several continents. Between 2019 and 2025, most human cases reported to the WHO occurred in the Democratic Republic of the Congo and in Madagascar, where bubonic plague is recorded almost every year. In the United States, the CDC counts an average of five human cases a year, mainly in northern New Mexico and Arizona: hikers, hunters, prairie dogs.

What has changed fits in a single word: antibiotics. Diagnosed early, plague can be treated, and early diagnosis saves lives. That is precisely why the real danger is no longer the bacterium, but delay — a distant clinic, a late test, a cough mistaken for the flu, and within forty-eight hours you are back in the fourteenth century.

Nearly seven centuries after Caffa, we therefore know exactly what kills us, where it sleeps, and how to cure it. We have kept the two inventions of the Black Death: isolation, which works, and the designated culprit, which does not work but brings relief. If the next epidemic finds us just as helpless, it will not be for lack of medicine. It will be for lack of having read our own archives.