Transcript
In 1346, on the Crimean coast, a Genoese trading port called Kaffa was under siege. The besieging army, a force of the Mongol Golden Horde under their khan Jani Beg, had been camped outside the walls for months. Then something strange and terrible began killing the soldiers faster than any defender could. Jani Beg's men were dying by the hundreds, swollen and feverish, dark blotches spreading across their skin. Unable to take the city by force, the khan ordered his engineers to load the plague-dead onto catapults and hurl them over the walls of Kaffa. What came over those walls would not stay in Crimea.
The Genoese merchants inside Kaffa watched their own people begin to die. They fled to their ships and sailed west across the Black Sea toward Constantinople. They did not know they were carrying the disease with them. The bacterium, Yersinia pestis, travelled in the fleas clinging to the rats in the ships' holds, and perhaps already in the breath of the sailors themselves. When the galleys reached Constantinople in the summer of 1347, the plague came ashore. It would not stop moving for seven years.
To understand how something so catastrophic could happen, you need to go back much further. The bacterium at the heart of this story is ancient. Genetic research suggests Yersinia pestis had been infecting humans in some form for thousands of years, with flea-borne strains appearing roughly four thousand years ago. Earlier outbreaks had already struck the Roman Empire. The plague of Justinian, which began in 541 and returned in waves for two centuries, was caused by the same pathogen. But the fourteenth-century outbreak was something different in scale, in speed, and in consequence.
The earliest confirmed victims of this particular strain were not in Crimea. In 2022, researchers analysing graves in the Chüy Valley of what is now Kyrgyzstan found tombstones with inscriptions in the Syriac language recording deaths from pestilence in 1338 and 1339. DNA extracted from the teeth of seven individuals at these cemeteries confirmed the presence of Yersinia pestis, and further analysis showed this was the direct ancestor of the strain that would devastate Europe and the Middle East. The origin point was not a vague rumour from the Far East. It was a specific place, a specific year, a specific burial ground.
This region sat at the heart of the Mongol Chagatai Khanate, one of four successor states carved from the empire built by Genghis Khan. The Mongols had created the most efficient long-distance communications network the medieval world had ever seen, a system of postal relay stations and protected trade routes stretching from China to the Black Sea. Merchants, diplomats, and soldiers moved along these routes constantly. It was, unintentionally, a perfect mechanism for carrying a disease across a continent. The plague spread where the Mongols had built their roads.
From Kyrgyzstan the bacterium moved west. It reached the Golden Horde's territories along the Volga River by 1346, devastating the Horde's capital and the urban centres of the western steppe. It struck the Mongol army besieging Kaffa. And when those infected galleys sailed from Kaffa toward Constantinople, the disease entered the Mediterranean world, a world of dense cities, busy ports, and trade routes connecting every corner of Europe and the Islamic world.
What Yersinia pestis did to a human body was documented with horrifying precision by survivors. The most common form, bubonic plague, announced itself with a high fever, aching joints, nausea, and the swelling of lymph nodes into hard, painful lumps called buboes, in the groin, armpits, or neck. The Florentine writer Boccaccio described some growing as large as an apple or an egg, oozing pus, and he noted the dark spots or blackened patches that spread across the skin. Left untreated, roughly four in five victims died within eight days.
But bubonic plague was not the only form. A second variety, pneumonic plague, infected the lungs directly and spread through the air between people. It was faster and even deadlier, with a mortality rate approaching ninety-five per cent. A third form, septicaemic plague, entered the bloodstream and was almost always fatal. Scholars now believe that the extraordinary speed of the epidemic's inland spread, far faster than rat fleas alone could account for, suggests the pneumonic form was spreading from person to person alongside the flea-borne route. The disease moved by multiple paths at once.
Medieval physicians and authorities were entirely without explanation. The Medical Faculty of Paris declared that a conjunction of planets had poisoned the air. Muslim scholars debated whether a God-sent pestilence should even be resisted. No one understood that the enemy was a bacterium. No one knew that the flea biting them in the night was the vector. No one could stop it.
From Constantinople the plague moved in every direction. By autumn 1347 it had reached Alexandria in Egypt, carried by a single merchant ship from Constantinople. Twelve Genoese galleys brought it to Sicily in October 1347. Further galleys reached Genoa and Venice in January 1348, and within weeks it had entered the Italian mainland through Pisa. Marseilles was infected by the end of January. From Italy it drove northwest: France, Spain, Portugal, and England all felt it by June 1348.
In England it came ashore and moved inland with terrible efficiency. In Norway it arrived in 1349 when a ship landed at Askøy, then spread to the city of Bergen. By 1350 it had swept through Germany and Scandinavia. Two years later it reached northern Russia, and by 1353 it had arrived in Moscow. The plague followed trade routes, coastlines, and river valleys. Isolated communities and areas with weak trade connections, parts of Poland, some Alpine villages, pockets of the Low Countries, tended to suffer less. But there were very few places that escaped entirely.
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The Middle East was struck with equal force. By late summer 1348, the plague had reached Cairo, then the largest city in the Mediterranean world, a metropolis of perhaps six hundred thousand people and the cultural capital of the Islamic world. More than a third of its residents died. The Nile was choked with corpses. The historian al-Maqrizi wrote of the abundant work for grave-diggers and of funeral rites performed in relentless succession. The disease then pushed south and east: Gaza, Damascus, Aleppo, Jerusalem, Antioch, Mecca, Baghdad, and the cities of the Yemen all fell within three years. Everywhere it went, it emptied cities.
The numbers are staggering enough that they risk becoming abstract, so it is worth holding them against specific places. Half of Paris, a city of roughly one hundred thousand people, died. Florence lost between half and four-fifths of its population within four months in 1348; its tax records suggest the carnage was almost total in certain quarters. At least three in five inhabitants of Hamburg and Bremen perished. London may have lost a similar proportion, with a death toll of around sixty thousand between 1346 and 1353. In Siena, the chronicler Agnolo di Tura wrote that he buried his five children with his own hands, that no one wept for any death because all awaited their own, and that people believed they were witnessing the end of the world.
Across Europe as a whole, historians estimate that between thirty and sixty per cent of the population died. The most careful assessments suggest something close to half. Pope Clement the Sixth's own agents, calculating in 1351, counted nearly twenty-four million dead in Christian Europe alone. The historian Ole Benedictow, working from available records, argues for a mortality rate of sixty per cent across the continent. Egypt lost roughly forty per cent of its population. The Middle East lost perhaps a third. In total, somewhere between seventy-five million and two hundred million people across Eurasia died in the pandemic. The fourteenth century had begun with about four hundred million people alive on Earth. It ended with far fewer.
The plague did not fall evenly. Cities suffered more than the countryside. The poor suffered more than the wealthy, already weakened by malnutrition after the Great Famine of 1315 to 1317, which had struck Europe a generation earlier. Clergy and religious orders suffered terribly because they tended the sick. Monks, nuns, and priests died in enormous numbers precisely because their duty brought them into direct contact with the dying. Monasteries emptied. Parish churches lost their priests. The institutional church, which had been the organising backbone of European society, was suddenly crippled.
The mass deaths required mass burials. Pits were dug outside cities and bodies stacked in them without ceremony, without priests, without the rites that medieval Christianity considered essential for the soul. Agnolo di Tura described the dead covered so sparsely with earth that dogs dragged bodies from the shallow graves and ate them in the streets of Siena. The normal rituals by which communities processed death, the prayers, the vigils, the processions, simply could not function when everyone was dying at once.
The plague shattered the economic order of Europe, but not in a single direction. For survivors, land suddenly became abundant. Rents collapsed. Labour became scarce, and wages rose sharply as landowners competed for the workers who remained. Serfs and labourers found themselves in a position they had never held before: they could negotiate, they could move, they could demand better terms. The rigid feudal hierarchy, in which a peasant's place was fixed by birth and obligation, began to crack under the pressure of demographic catastrophe.
The disruption to the Mongol Empire was equally severe. The plague killed the merchants and officials who maintained the Silk Road trade network. It decimated the administrative class of the Golden Horde and the Ilkhanate, the Mongol rulers of Persia, triggering civil wars and political collapse. The Golden Horde entered a period of prolonged internal conflict beginning in 1359, known as the Great Troubles, which fatally weakened its grip on its Russian vassals and eventually allowed the rise of the Grand Duchy of Moscow. The Yuan Dynasty in China, already under pressure from famine and flooding, faced the Red Turban Rebellion from around 1351, and fell in 1368 when the Ming Dynasty replaced it.
The persecution of Jewish communities across Europe during the plague years was one of the most shameful consequences of the catastrophe. Unable to explain the disease, many Europeans blamed Jews for poisoning wells. In February 1349, around two thousand Jews were murdered in Strasbourg. In August of that year, the Jewish communities of Mainz and Cologne were annihilated. By 1351, sixty major and one hundred and fifty smaller Jewish communities had been destroyed. Many survivors fled eastward to Poland, where King Casimir the Great offered them protection.
The word quarantine was born in this era. The city-state of Ragusa, modern Dubrovnik, implemented a thirty-day isolation period in 1377 for anyone arriving from plague-affected areas. The period was later extended to forty days, and the practice was named quarantino, from the Italian word for forty. It was one of the first systematic public health measures in European history, and the word has remained in use ever since.
The Black Death's cultural consequences took generations to unfold. Some historians have argued that the devastation of Florence between 1348 and 1350, and the resulting intimacy with death, pushed Italian thinkers toward a new preoccupation with earthly life rather than the afterlife, contributing to the conditions that produced the Renaissance. Religious sensibility shifted: the old institutional certainties gave way to more personal, inward forms of devotion. New guilds and lay religious movements sprang up. Church decoration became more elaborate, almost compulsive, as survivors sought to fill the silence left by the dead.
The plague did not end in 1353. It returned. According to the historian Jean-Noël Biraben, the disease was present somewhere in Europe in every single year between 1346 and 1671. The second pandemic recurred in major waves through the fifteenth, sixteenth, and seventeenth centuries. France alone lost at least two million people to plague between 1600 and 1670. Italy lost around one and a half million in the first half of the seventeenth century. The Ottoman capital of Constantinople recorded dozens of separate epidemics between 1700 and 1800. Cairo suffered more than fifty plague outbreaks in the century and a half after the first visitation, with the final wave of the second pandemic arriving there only in the 1840s.
Each successive wave of the plague, however, killed fewer people. A physician serving the papal court at Avignon, writing in 1382, observed that in the first outbreak two thirds of those infected died; by the second, only some; by the third, a tenth were affected and many survived. By the end of the fourteenth century, the disease was killing primarily children, suggesting that adults who had survived earlier outbreaks were carrying some degree of resistance. The epidemic was slowly, generation by generation, changing the immune profile of the European population.
A third pandemic began in China in the mid-nineteenth century and spread to all inhabited continents, killing ten million people in India alone. It was during this outbreak, in Hong Kong in 1894, that the French-Swiss bacteriologist Alexandre Yersin, a pupil of Louis Pasteur, identified the bacterium responsible. It was named Yersinia pestis in his honour. A few years later, another scientist established the mechanism: fleas whose digestive systems had become blocked by replicating bacteria bit aggressively to try to clear the blockage, and in doing so flushed thousands of plague bacteria into the wound. The medieval world's great invisible killer finally had a name and a face.
The populations of some Italian cities, including Florence, did not return to their pre-plague levels until the nineteenth century. That is roughly five hundred years of demographic deficit, five centuries in which the shadow of a single pandemic lay across the land. The bacterium that Agnolo di Tura blamed on no one and everything, that the Paris physicians blamed on the stars, that frightened communities blamed on the Jews, was a microorganism spread by fleas, moving through breath and blood, indifferent to prayers and accusations alike. It killed half a continent because no one knew what it was, and the world it left behind had to be built almost from the beginning.
Modern antibiotics can treat plague effectively, reducing the fatality rate from something close to eighty per cent to around eleven per cent. Small outbreaks still occur, in Madagascar, in parts of Central Asia, in the western United States, where the bacterium persists in rodent populations just as it has for thousands of years. The graves in Kyrgyzstan, the catapults at Kaffa, the galleys sailing into Messina harbour in October 1347: what they set in motion has not fully stopped. The disease that buried five children in Siena, that emptied the streets of Cairo, that broke the feudal order of Europe and gave us the word quarantine, still moves quietly through the animals of the grasslands, waiting.
Image: Pieter Brueghel the Elder, Public domain · AI-narrated · Drawn from Wikipedia · CC BY-SA 4.0
