The Black Death was the first and deadliest wave of what historians call the second plague pandemic. From the late 1340s into the early 1350s it moved out of central Eurasia, through the Black Sea and the Mediterranean, and across 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 burials matches the bacterium and sits near the root of later plague lineages.
A 2022 study in Nature analysed remains from cemeteries at Kara-Djigach and Burana in the Tian Shan region of what is now Kyrgyzstan. Tombstones there record a “pestilence” in 1338–39. The reconstructed genomes represent a strain ancestral to the diversification linked to the pandemic. Modern Y. pestis in marmot reservoirs in the wider Tian Shan still sit close to that ancestral position. The older line that the disease simply “started in China in 1334” is too neat. Trade, climate, and rodent ecology all matter. The best current genetic evidence points to an emergence in central Eurasia in the early fourteenth century, a few years before the disease appeared in force on the western steppe and the Black Sea.
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 in the orbit of the Genoese port of Kaffa (now Feodosia) in Crimea. A later Italian account by Gabriele de’ Mussi described Mongol forces hurling plague corpses over Kaffa’s walls. De’ Mussi was not there, and specialists now treat that corpse-catapult 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, infected rats, fleas, and people moved with cargo. Italian ports recorded outbreaks in 1347. By 1348 the disease was in France, the Iberian Peninsula, England, and much of the Islamic Middle East. Recurrences followed for centuries. The second pandemic did not end after one five-year wave.
Y. pestis is transmitted mainly by fleas that live on rodents. When rodent hosts die, fleas seek other mammals, including humans. The classic bubonic form produces painfully swollen lymph nodes (buboes), fever, and, in a high share of untreated historical cases, death. Pneumonic plague spreads person to person through respiratory droplets and is faster and still more lethal. Septicemic plague infects the blood. Medieval observers described swellings, dark skin discoloration 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.
Mortality estimates vary because medieval sources are uneven and because the disease did not strike every region with equal force. A long-standing popular figure is that about one-third of Europe’s population died. Demographic reconstructions that compile local studies, notably the work of Ole J. Benedictow, argue that mortality in much of Europe was closer to 60 percent. Other research, including palaeoecological work that uses pollen as a proxy for farming, finds strong spatial differences: some regions 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 following 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.
Immediate social effects followed from the sudden scarcity of labour. 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. The English Ordinance and Statute of Labourers (1349–51) attempted 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 institutional 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 flipped medieval society into modernity.
Religious and cultural effects were large and mixed. Flagellant processions, persecution of Jewish communities blamed for well-poisoning, 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 through 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 influenced 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 determined 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 clarified 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 underway. Those are live research questions. The core facts are not: a Y. pestis strain that emerged in central Eurasia in the early fourteenth century travelled west with people, goods, and rodents and killed a very large share of the population in the societies it reached.
SOURCES: Nature, Britannica, Council on Foreign Relations-level historical summaries, BBC History, EH.net, Journal of Economic Literature, Nature Ecology & Evolution, Communications Earth & Environment.
