The Black Death — the mid-14th-century pandemic that killed perhaps 30–60 % of Europe’s population — is among the most devastating tragedies in human history. For decades, popular memory and many historical accounts depicted it as a tale of black rats, fleas, and filth: rats infested medieval towns, fleas carrying the plague bacterium jumped to humans, and the disease ripped through Europe with devastating speed. But in recent years, historians, archaeologists and climate scientists have built a radically more complex—and compelling—story. The plague may have arrived via far-flung trade, carried not by familiar city rats, but through rodents and fleas from Central Asia — and the trigger might well have been a volcanic eruption that disrupted climate, food supply and trade patterns.
Below is a timeline of how our understanding of the origins and spread of the Black Death has shifted over time — culminating in the landmark 2025 study that posits a “perfect storm” of volcanic, climatic, economic and epidemiological factors.
1. The early model: rats, fleas — and folklore about cats
Since the late 19th and early 20th centuries, the dominant explanation for the Black Death has been that the bacterium Yersinia pestis was transmitted by fleas living on rodents common in medieval Europe — chiefly the black rat (ship-rat), Rattus rattus. Fleas would bite infected rats, then bite humans, transmitting plague. This “rat-and-flea model” offered a neat biological mechanism that matched the speed and scale of the epidemic. Wikipedia+2The New Yorker+2
Beyond rats and fleas, folklore and post-pandemic myth added a dramatic layer: stories of mass killings of cats. According to a popular narrative, cats (especially black cats) had been associated with the devil or witchcraft, and in fear or superstition, many were slaughtered — removing a natural predator of rats, thus allowing rat populations to explode and accelerate the plague’s spread. Some versions even tie this to earlier church decrees such as the 13th-century papal bull Vox in Rama, which condemned certain heretical sects alleged to worship cats or other creatures.
However: modern historians and epidemiologists have largely debunked this “cats-killed → rats flourish → plague worsened” story. There is no credible contemporary evidence of widespread, coordinated massacres of cats across medieval Europe, nor documentation linking such actions to a surge in rat populations or to plague outbreaks. Moreover, cats themselves are susceptible to plague; killing them would not necessarily reduce plague risk and might even remove animals that could have helped curb rodents — but would not have stopped fleas or infected rodents. Reddit
Thus, historians now treat the “cat-pocalypse worsened the plague” story more as modern myth than as credible history — a cautionary example of how legends can attach themselves to tragic events long after the fact.
2. The rat-and-flea model takes root — with growing doubts
Through much of the 20th century, the rat/flea explanation remained dominant. That made sense: Europe had rats in plenty; medieval towns were crowded and unhygienic; flea infestations were plausible; and once introduced, plague could spread rapidly among rodents and from rodents to humans. Many outbreaks after the Black Death — recurrent “plague waves” over centuries — appeared compatible with this model.
Nevertheless, as scholars looked more closely at ecology, climate, and the geographical distribution of rodents, doubts began to emerge. Questions such as “Why did plague flare up in certain years, then subside?” or “Could European rodent populations alone sustain plague over centuries?” led some to argue that perhaps the rat-and-flea model was incomplete. PNAS+2The New Yorker+2
3. A shift in focus: rodents from Asia — gerbils, marmots and repeated re-introductions
In the last decade, a major re-evaluation occurred. A 2015 study from researchers (notably at the University of Oslo) argued that the primary long-term reservoirs of plague were not European rats, but wild rodents in Central Asia — in particular the Great gerbil (and possibly marmots or ground squirrels) — whose fleas could carry Y. pestis. PNAS+2The Guardian+2
According to this “gerbil-origin” hypothesis:
- Climate fluctuations in Asia — for example wet springs followed by warm summers — led to boom cycles in gerbil populations, which expanded fleas and increased transmission among rodents.
- When the rodent populations crashed (due to drought or other stress), fleas would seek new hosts — potentially humans, livestock or animals used in trade caravans. This could lead to pockets of infection among humans along trade routes, long before plague reached Europe.
- Historical data suggest that plague outbreaks in Europe often followed climate events in Asia by a number of years — consistent with repeated re-introductions, rather than a single European reservoir maintaining the plague for centuries.
This model does not necessarily exonerate rats — once plague reached Europe, rats and their fleas may well have helped propagate it — but it challenges the idea that Europe was a self-sustaining plague reservoir over centuries. Instead, plague might have been continually re-imported from Asia via trade routes.
This shift was significant: it recast the Black Death and subsequent plague outbreaks not as purely European phenomena, but as part of a broader trans-Eurasian ecology — a story of rodents, fleas, climate and trade.
4. The 2025 “perfect storm” hypothesis: volcanoes, famine, grain imports — and the spark that ignited the catastrophe
Building on the gerbil-origin theory and ecological data, a brand-new study (published December 2025 in the journal Communications Earth & Environment) from researchers at the University of Cambridge and the Leibniz Institute for the History and Culture of Eastern Europe (GWZO) proposes a more complete explanation — one that ties together climate, trade, famine and disease into a causal chain.
The chain of events
- Volcanic eruption around 1345: The team found evidence — in the form of sulphur and ash layers in polar ice cores and in tree-ring data from Europe — of a major volcanic eruption (or possibly multiple eruptions) around 1345, likely in the tropics.
- Climate disruption and crop failure: The volcanic aerosols would have reflected sunlight, plunging much of southern Europe and the Mediterranean into cooler, cloudier and wetter summers for several years. Tree rings from multiple European regions show stunted growth in 1345–1347, and contemporary accounts mention ominous skies, darkened sun or moon, and crop failures.
- Famine and grain imports: Facing starvation, powerful maritime city-states in Italy (such as Venice, Genoa and Pisa) turned to grain imports from farther afield — specifically from Black Sea/Sea of Azov regions under the control of the Golden Horde. Grain shipments began in 1347.
- Unintended import of plague: The 2025 study argues that those grain shipments likely carried more than food: they may have carried infected fleas (or rodents) — possibly arriving from Asia via the Black Sea — that were harboring Y. pestis. When those ships docked in Mediterranean ports, the plague had a foothold. Fleas would transfer to other rodents (or directly to humans), initiating the pandemic in Europe.
In short: a volcanic eruption triggered a climate shock → crop failures → famine → grain trade from plague-endemic areas → arrival of plague in Europe.
The authors suggest that this “perfect storm” mechanism — combining environmental, economic, ecological and social factors — may explain why the Black Death happened when it did, and why it spread so rapidly and devastatingly.
5. What this new scenario changes — and what remains uncertain
What’s strengthened
- Timing: The 1345 eruption provides a natural explanation for why a disaster of this magnitude occurred in the 1340s — not earlier, not later. The climatic data, contemporary records and trade behaviour align closely.
- Import route: Rather than supposing a stable European plague reservoir, this scenario highlights long-distance trade as the vector — black-sea grain shipments inadvertently brought plague to Europe.
- Ecological realism: It builds on previous work suggesting an Asian origin for the bacterium’s reservoirs (gerbils, marmots, etc.), rather than solely European rats.
What remains debated or unclear
- The exact location (or locations) of the 1345 volcanic eruption remains unknown; scientists only detect sulfate/aerosol signals in ice-cores, not a definitive volcano.
- It’s uncertain precisely how plague travelled on the grain-ships — via fleas, rodents, or dust — and how many fleas/rodents survived the journey. Scholars have not (yet) discovered direct contemporary records describing plague-infested grain arriving in Mediterranean ports.
- Once in Europe, how much the plague spread via European rats/fleas vs. other rodents or humans is still not fully understood — but the new hypothesis does not deny the role of European rodents, only that they likely were not the original or sole reservoir.
6. Why the “cats slaughtered → rat plague explosion → Black Death worsened” story persists — and why it’s considered myth
The notion that medieval cat killings worsened the Black Death has persisted partly because it offers a morally resonant narrative: superstition, persecution, and cruelty lead to catastrophe. It also ties into familiar tropes (black cats, witchcraft, evil). However, careful historical scholarship paints a different picture.
- The supposed papal decree “Vox in Rama” — often cited as evidence of Church-sanctioned cat extermination — does not in fact order mass cat killings; it references a specific heretical sect and does not generalize to all cats.
- Archaeological studies find no evidence for continent-wide declines in cat populations or coordinated mass slaughter in the period immediately preceding the Black Death. Museum Hack+2talesoftimesforgotten.com+2
- Moreover, cats themselves can contract plague, and so are not an unambiguous “good guy” — killing them might not have helped, and could even have removed animals that helped control rodents, but it wouldn’t have blocked flea transmission. Wikipedia+1
In other words: the cat-massacre story remains more legend and modern myth than based on solid contemporary evidence.
7. What this evolving understanding teaches us — and why it matters
The 2025 “volcano–famine–trade–plague” hypothesis does more than rewrite a chapter of medieval history — it offers a powerful example of how multiple risk factors can combine in unexpected ways to produce a catastrophic pandemic.
- It shows how climate events (volcanic eruptions) can set off cascading effects — agricultural collapse, famine, social stress — that reshape trade and human movement.
- It underscores the danger of globalised trade: in times of crisis, societies may import essential goods — but trade can also transport pathogens, fleas, rodents and other hidden risks.
- It also illustrates the value of interdisciplinary research — combining climatology (ice-cores, tree rings), historical records, epidemiology, archaeology and ecology — to re-examine long-held assumptions.
In a world where climate change, global trade and rapid travel remain defining characteristics — the parallels are sobering. The Black Death did not arise simply from medieval squalor or superstition; it may have been the tragic result of environmental disaster colliding with global commerce, executed via ecological and epidemiological pathways.
8. Conclusion: a new — and more nuanced — narrative of the Black Death
For centuries, the Black Death has been told as a tale of rats, fleas, filth — and sometimes superstition-driven cruelty to cats. While this simplified narrative captured public imagination, it never fully accounted for why the pandemic happened when it did, or why it spread so explosively across such different climates and regions.
The evolving scholarship — culminating in the 2025 study — offers a richer, more complex picture: one in which a volcanic eruption triggers climate disruption; in which famine forces trade; in which grain ships become vectors; and in which plague travels not because Europe was already crawling with plague-bearing rodents, but because global trade routes connected distant ecological reservoirs of disease.
In short, the Black Death may not just have been a medieval “disease of rats” — it may have been one of history’s first great climate-driven, globalization-enabled pandemics.
Sources: as shown plus lots more including Nature Asia and Reddit to name 2. My thanks to The Times newspaper of 5th December 2025 for reporting on the Cambridge University research which prompted a review of the causes of the Black Death in medieval times.
