The Black Death was the first and deadliest wave of the second plague pandemic. In the late 1340s and early 1350s it spread from central Eurasia through the Black Sea and the Mediterranean into large parts of Europe, the Middle East, and North Africa. It was caused by the bacterium Yersinia pestis. That is no longer a guess. Ancient DNA from dated fourteenth-century graves matches the bacterium and sits near the root of later plague lineages.
A 2022 study in Nature examined graves at Kara-Djigach and Burana in the Tian Shan mountains of what is now Kyrgyzstan. Tombstones there say people died of a “pestilence” in 1338–39. The bacteria from those graves belong to an ancestral lineage of Y. pestis. The lineage associated with the Black Death emerged from this branch of the plague bacterium.
Modern Y. pestis populations in plague reservoirs across the wider Tian Shan region also contain closely related lineages, supporting the idea of a local emergence. The older claim that the disease simply “started in China in 1334” is too neat. Trade, climate, and rodent ecology all played roles. Current genetic evidence instead points to an emergence of the lineage associated with the Black Death somewhere in central Eurasia in the early fourteenth century, before it spread westward onto the steppe and eventually reached the Black Sea region.
How it entered Europe is clearer in outline than in every local scene. Plague was present around the Black Sea in 1346–47, including among peoples of the Golden Horde and near the Genoese port of Kaffa (now Feodosia) in Crimea. A later Italian account by Gabriele de’ Mussi said Mongol forces hurled plague corpses over Kaffa’s walls. De’ Mussi was not there. Specialists now treat that story as unproven and, in some readings, implausible. What is better supported is more ordinary and more important: when shipping between the Black Sea and the Mediterranean resumed, rats, fleas, people, and potentially infected goods provided routes for the disease to move west. Italian ports recorded outbreaks in 1347. By 1348 the disease was in France, the Iberian Peninsula, England, and much of the Islamic Middle East. Later waves followed for centuries. The second pandemic did not end after one five-year surge.
Y. pestis is transmitted mainly by fleas that live on rodents. When those rodent hosts die, the fleas seek other mammals, including people. The classic bubonic form produces painfully swollen lymph nodes (buboes), fever, and, in a high share of untreated historical cases, death. Pneumonic plague spreads from person to person through respiratory droplets and is faster and still more lethal. Septicemic plague infects the blood. Medieval writers described swellings, dark skin from bleeding under the skin, and sudden death. They did not know the bacterium or the flea–rat cycle. Those were established in the late nineteenth century, beginning with Alexandre Yersin’s identification of the organism in 1894.
Death-toll estimates vary. Medieval sources are uneven, and the disease did not hit every region with equal force. A long-standing popular figure is that about one-third of Europe’s population died. Demographic work that compiles local studies, notably by Ole J. Benedictow, argues that mortality in much of Europe was closer to 60 percent. Other research, including palaeoecological studies that use pollen as a proxy for farming, finds sharp regional differences: some areas show a collapse of cultivation consistent with very high death rates; others show little change. England’s population is often estimated to have fallen by around half and to have recovered only slowly over the next two centuries. Urban and clerical records sometimes show even higher local losses. No single percentage should be treated as exact for “Europe” as a whole. Tens of millions of people died in a few years. That is not in dispute. The precise continental average is.
The sudden shortage of labour had immediate social effects. In much of western Europe, real wages for rural and urban workers rose in the decades after 1348. Land became relatively more abundant. Some settlements were abandoned. In parts of England, arable land shifted toward pasture and wool. Landlords tried to hold wages and services down; labourers tried to move and bargain. England’s Ordinance and Statute of Labourers (1349–51) tried to freeze wages at pre-plague levels. Enforcement was incomplete. Whether the plague “ended feudalism” is a matter of interpretation. In England and some other western regions, labour services and serfdom declined over the following generations. In parts of eastern Europe, landlords and rulers later tightened peasant obligations—the opposite response to the same labour shortage. The plague was a massive demographic shock that interacted with existing institutions. It was not a single switch that turned medieval society into the modern world.
Religious and cultural effects were large and mixed. Flagellant processions, attacks on Jewish communities blamed for poisoning wells, and intense concern with death and salvation appear in the sources. So does continuity: churches still functioned, governments still collected taxes where they could, and trade resumed. Later waves in the fifteenth, sixteenth, and seventeenth centuries kept populations below pre-1340s peaks in many areas and repeated the cycle of fear, flight, and local quarantine.
Climate may have affected the timing. Recent work links a mid-1340s downturn—cooler, wetter seasons, possibly tied to volcanic sulfur in the atmosphere—to poor Mediterranean harvests and to Italian grain imports from the Golden Horde around the Sea of Azov in 1347. On that reading, ships that eased famine also moved infected fleas with the grain. That is a plausible contributing mechanism, not a complete explanation and not yet a consensus. Plague ecology depends on rodent reservoirs, flea biology (temperature and humidity affect flea activity), and human movement. Trade routes were the highways. Climate and harvest stress may have decided when those highways were busiest.
The Black Death did not invent poverty, religious anxiety, or wage conflict. It made labour scarce on a scale medieval Europe had not seen. Genetic evidence has identified the pathogen and narrowed the likely geographic origin. Historical and archaeological evidence has shown that the impact was devastating in many places and uneven in others. What remains uncertain is the exact death toll in poorly documented regions, the full list of environmental triggers, and how much of later economic divergence in northwestern Europe should be credited to the plague rather than to slower institutional and commercial changes already under way. Those are live research questions. The core facts are not in dispute: a lineage of Y. pestis associated with the Black Death emerged in central Eurasia in the early fourteenth century, spread west through people, trade, animals, and goods, and killed a very large share of the populations in the societies it reached.
SOURCES: Nature; Britannica; BBC History; EH.net; Journal of Economic Literature; Nature Ecology & Evolution; Communications Earth & Environment.
