The Black Death: How a Pandemic Moved and Who It Missed

The Black Death was an outbreak of plague, caused by the bacterium Yersinia pestis, that reached the Mediterranean world in the late 1340s and killed an enormous but very unevenly distributed number of people. Genomic work published in Nature in 2022 traced the most recent common ancestor of the pandemic strain to burials near Lake Issyk-Kul, in what is now Kyrgyzstan, where tombstone inscriptions record an epidemic in 1338-1339. What followed was not one uniform catastrophe across one continent: mortality varied sharply from place to place, the pandemic ran through the Middle East and North Africa as well as Europe, and in 1348 and 1349 it became the pretext for the mass murder of Jewish communities.

Where the strain came from, and what the evidence actually shows

For centuries the origin of the Black Death was argued from chronicles alone. That changed when ancient DNA became recoverable from medieval teeth.

The 2022 Nature study examined burials from two cemeteries, Kara-Djigach and Burana, near Lake Issyk-Kul in present-day Kyrgyzstan. Tombstones there date a local epidemic to 1338-1339. The researchers recovered two ancient Y. pestis genomes and concluded that they "represent a single strain and are identified as the most recent common ancestor of a major diversification commonly associated with the pandemic's emergence". They describe their method as a synthesis of archaeological, historical and ancient genomic data, and place the pandemic's arrival in the Black Sea region around 1346.

It is worth being precise about what that does and does not establish. The genomes date the ancestry of the lineage; the tombstones date a local epidemic; the two agree, which is why the argument is strong. It is not a claim that one village infected a continent, and it does not settle every question about the routes the disease took afterwards. Separating what a piece of evidence proves from what it is merely consistent with is the core skill in this subject, and the same discipline is what makes the long argument over what caused the Bronze Age collapse tractable rather than merely noisy.

What plague is, and why the biology changes the history

Plague is a zoonotic disease: it lives in small mammals and their fleas and spills over into people. The World Health Organization describes three routes of human infection — the bite of an infected vector flea, unprotected contact with infectious bodily fluids or contaminated material, and the inhalation of respiratory droplets from a patient with pneumonic plague. The Centers for Disease Control and Prevention notes that people most often become infected "through the bite of an infected rodent flea or by handling an infected animal", and that plague can be cured with antibiotics if they are given promptly.

Those routes behave differently, and that is a historical fact as much as a medical one. Flea-borne transmission follows rodents, grain, cloth and ships, which is why the pandemic tracks commercial routes. Pneumonic transmission passes directly between people and moves much faster; the WHO notes that its incubation can be as short as 24 hours and that it is "invariably fatal unless treated early". A chronicler describing a town emptying within days and a chronicler describing a slow seasonal grind may both be accurate and describing different mechanisms.

Why a single death rate cannot describe the pandemic

The WHO estimates that the fourteenth-century Black Death caused more than 50 million deaths in Europe. That is a large-scale estimate, and it should be quoted as one.

Proportional figures — a third, a half, six in ten — are far more fragile, because a percentage needs two numbers, and the population before the plague is itself reconstructed from tax rolls, manorial surveys and wills rather than counted. Where those records are serial and well preserved, historians can say a great deal. Where they are thin or lost, they cannot, and the honest answer is a range.

This matters for how you read any confident sentence about the Black Death. A figure derived from a Tuscan city with exceptional notarial records is not evidence about rural Poland, and it is not evidence about Cairo. The pandemic's course through the Middle East and North Africa is studied in the scholarly literature and almost entirely absent from the popular version, which is a gap in teaching rather than in the sources. Our guide to how historians date events covers the record-linkage methods that produce these estimates in the first place.