The Great Mortality: An Intimate History of the Black Death, the Most Devastating Plague of All Time

by John Kelly

The plague generation wrote about their experiences with a directness and urgency that, seven hundred years after the fact, retains the power to move, astonish, and haunt. After watching packs of wild dogs paw at the newly dug graves of the plague dead, a part-time tax collector in Siena wrote, “This is the end of the world.” His contemporaries provided vivid descriptions of what the end of the world looked like, circa 1348 and 1349.

In a century when nothing moved faster than the fastest horse, the Black Death had circumnavigated Europe in a little less than four years.

To the Mongols, the Genoese seemed vainglorious, supercilious, and deeply duplicitous, the kind of people who would name their children after you—as the Dorias of Genoa had named three sons after three Mongol notables; Huegu, Abaka, and Ghazan—while picking your pocket.

When the founder of the Mongol empire, Genghis Khan, railed against “eaters of sweet greasy food [who wear] garments of gold . . . [and] hold in their arms the loveliest of women,” he might have had the Genoese in mind.

Most modern historians believe that what we call the Black Death originated somewhere in inner Asia, then spread westward to the Middle East and Europe and eastward to China along the international trade routes. One frequently mentioned origin point is the Mongolian Plateau, in the region of the Gobi desert where Marco Polo says the night wind makes “a thousand fantasies throng to mind.”

“Stunned and stupefied” by the arrival of the plague, the notary says that the Tartars “ordered corpses to be placed in catapults and lobbed into the city in hopes that the intolerable stench would kill everyone inside. . . . Soon rotting corpses tainted the air . . . , poisoned the water supply, and the stench was so overwhelming that hardly one man in several thousand was in a position to flee the remains of the Tartar army.”

Today a demographic disaster on the scale of the Black Death would claim 1.9 billion lives.

Plague is among the slowest moving of wandering sicknesses. New strains of influenza can leap around the world in a year or two, but Y. pestis, like the AIDS virus, is tied to a complicated chain of infection that can take decades to unfold. The principal vector in the disease is not the rodent, the animal most often associated with it, but the rodent flea. When an infected host dies, the flea leaps to a new host, transferring the plague bacillus, Y. pestis, to the host by way of a skin bite. Sometimes humans are infected directly by one of the many flea species that prey on wild rodents, such as squirrels, prairie dogs, and marmots; however, most often the agent of infection in human plague is the more familiar black rat flea, Xenopsylla cheopis.

Malodorousness was another frequent symptom of historic bubonic plague. Victims not only looked as if they were about to die, according to many Black Death chroniclers, they often smelled as if they were. After visiting a plague-stricken friend, one man wrote, “The stench [of] sweat, excrement, spittle, [and] breath [was] overpowering.”

A third theory, not incompatible with the first two, is that epizootics are activated by surge years—sudden, dramatic spurts in the rodent population. No one is sure what causes surges, but a number of scientists believe that they may be related to sun spots, which follow roughly the same cyclical pattern as surge years in many (though not all) rodent species, approximately ten to twelve years.

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A recent study of two thousand years of tree ring data reveals that four years in the last two millennia were periods of extraordinarily severe weather, and two of those four years were situated in or around a plague pandemic. One was 1325, roughly the time Y. pestis may have been at work on the rodent population of the Gobi or some other region of inner Asia; the other was 540, two years before Y. pestis arrived in Pelusium, and roughly around the time that Chinese scribes were describing yellow dust falling like snow and Europeans were complaining about the bitter cold that ushered in the Dark Ages. “The winters [are] grievous and more severe than usual,” wrote the sixth-century monk Gregory of Tours.

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At its height, the city of Rome had a population variously estimated at half a million to ten million; by 800, no city in Europe contained more than twenty thousand residents. “In the middle of the debris of great cities,” wrote one Dark Ages scribe, “only scattered groups of wretched peoples survive.”

Between 1250 and 1270 the long medieval boom sputtered to an end. One of the great ironies of the Black Death is that it occurred just as the medieval global economy, the vehicle of Y. pestis’s liberation, was nearing collapse. However, in Europe, it was the implosion of the vastly larger domestic economy, particularly the agricultural economy, that people felt most keenly. The implosion was continentwide, but in England, a nation of meticulous record keepers, it was documented with great diligence. Around 1300 the acreage under plow decreased, while the land still in use either declined in productivity or stagnated. After centuries of heady advancement, the medieval peasant’s mistakes had caught up with him. Some of the good land brought into service during the Great Clearances of the twelfth century had been overfarmed, and some of the more marginal land, which never should have been cleared in the first place, was giving out entirely.

Rather than a reckoning, the image of postboom Europe that comes to mind is that of a man standing up to his neck in water. Drowning may not be inevitable, but the man’s position is so fraught, even a very slight rise in the next tide could kill him. As Dr. Herlihy asserts, a crowded Europe may well have been able to hang on for “the indefinite future,” but, like the man in the water, after the land gave out and the economy collapsed, the continent had no margin for error. Just to continue keeping its head above water, everything else had to go right, and in the early fourteenth century, a great many things began to go terribly wrong, beginning with the climate.

“By inference,” declares Professor Jordan, author of a study on the Great Famine, “the horrendous mortality of the Black Death should reflect the fact that poor people who were in their thirties and forties during the plague had been young children in the period 1315–1322 and were developmentally more susceptible to the disease than those who had been adults during the Famine or were born after the Famine abated.”