Causes Early theory A report by the Medical Faculty of Paris stated that a conjunction of planets had caused "a great pestilence in the air" (
miasma theory). Muslim religious scholars taught that the pandemic was a "martyrdom and mercy" from God, assuring the believer's place in paradise. For non-believers, it was a punishment. Some Muslim doctors cautioned against trying to prevent or treat a disease sent by God. Others adopted preventive measures and treatments for plague used by Europeans. These Muslim doctors also depended on the writings of the ancient Greeks.
Predominant modern theory Due to
climate change in Asia, rodents began to flee the dried-out grasslands to more populated areas, spreading the disease. The plague disease, caused by the bacterium
Yersinia pestis, is
enzootic (commonly present) in populations of fleas carried by ground
rodents, including
marmots, in various areas, including
Central Asia,
Kurdistan,
West Asia,
North India,
Uganda, and the western United States.
Y. pestis was discovered by
Alexandre Yersin, a pupil of
Louis Pasteur, during an
epidemic of bubonic plague in Hong Kong in 1894; Yersin also proved this bacterium was present in rodents and suggested the rat was the main vehicle of transmission. The mechanism by which
Y. pestis is usually transmitted was established in 1898 by
Paul-Louis Simond and was found to involve the bites of fleas whose
midguts had become obstructed by replicating
Y. pestis several days after feeding on an infected host. This blockage starves the fleas, drives them to aggressive feeding behaviour, and causes them to try to clear the blockage via
regurgitation, resulting in thousands of plague bacteria flushing into the feeding site and infecting the host. The bubonic plague mechanism was also dependent on two populations of rodents: one resistant to the disease, which act as
hosts, keeping the disease
endemic, and a second that lacks resistance. When the second population dies, the fleas move on to other hosts, including people, thus creating a human
epidemic.
DNA evidence , near
Marseille in southern France, yielded molecular evidence of the
orientalis strain of
Yersinia pestis, the organism responsible for bubonic plague. The second pandemic of bubonic plague was active in Europe from 1347, the beginning of the Black Death, until 1750. Definitive confirmation of the role of
Y. pestis arrived in 2010 with a publication in
PLOS Pathogens by Haensch et al. They assessed the presence of
DNA/
RNA with
polymerase chain reaction (PCR) techniques for
Y. pestis from the
tooth sockets in human skeletons from mass graves in northern, central and southern Europe that were associated archaeologically with the Black Death and subsequent resurgences. The authors concluded that this new research, together with prior analyses from the south of France and Germany, "ends the debate about the cause of the Black Death, and unambiguously demonstrates that
Y. pestis was the
causative agent of the epidemic plague that devastated Europe during the Middle Ages". In 2011 these results were further confirmed with genetic evidence derived from Black Death victims in the
East Smithfield burial site in England. Schuenemann et al. concluded in 2011 "that the Black Death in medieval Europe was caused by a variant of
Y. pestis that may no longer exist". Later in 2011,
Bos et al. reported in
Nature the first draft genome of
Y. pestis from plague victims from the same East Smithfield cemetery and indicated that the strain that caused the Black Death is ancestral to most modern strains of
Y. pestis. Later genomic papers have further confirmed the
phylogenetic placement of the
Y. pestis strain responsible for the Black Death as both the ancestor of later plague epidemics—including the
third plague pandemic—and the descendant of the strain responsible for the
Plague of Justinian. In addition, plague genomes from prehistory have been recovered. DNA taken from 25 skeletons from 14th-century London showed that plague is a strain of
Y. pestis almost identical to that which
hit Madagascar in 2013. Further DNA evidence also proves the role of
Y. pestis and traces the source to the
Tian Shan mountains in
Kyrgyzstan.
Alternative explanations Researchers are hampered by a lack of reliable statistics from this period. Most work has been done on the spread of the disease in England, where estimates of overall population at the start of the plague vary by over 100%, as no census was undertaken in England between the time of publication of the
Domesday Book of 1086 and the
poll tax of the year 1377. Estimates of plague victims are usually
extrapolated from figures for the clergy.
Mathematical modelling is used to match the spreading patterns and the means of
transmission. In 2018 researchers suggested an alternative model in which "the disease was spread from human fleas and body lice to other people". The second model claims to better fit the trends of the plague's death toll, as the rat-flea-human hypothesis would have produced a delayed but very high spike in deaths, contradicting historical death data. The Oriental rat flea has poor survival in cooler climates and reevaluation suggests the
human flea was the principal vector of plague epidemics in Northern Europe.
Lars Walløe argued that these authors "take it for granted that Simond's infection model, black rat → rat flea → human, which was developed to explain the spread of plague in India, is the only way an epidemic of
Yersinia pestis infection could spread". Similarly,
Monica Green has argued that greater attention is needed to the range of (especially non-
commensal) animals that might be involved in the transmission of plague. Archaeologist Barney Sloane has argued that there is insufficient evidence of the extinction of numerous rats in the archaeological record of the medieval waterfront in London, and that the disease spread too quickly to support the thesis that
Y. pestis was spread from fleas on rats; he argues that transmission must have been person to person. This theory is supported by research in 2018 which suggested transmission was more likely by body lice and
fleas during the
second plague pandemic.
Summary Academic debate continues, but no single alternative explanation for the plague's spread has achieved widespread acceptance. Many scholars arguing for
Y. pestis as the major agent of the pandemic suggest that its extent and symptoms can be explained by a combination of bubonic plague with other diseases, including
typhus,
smallpox, and
respiratory infections. In addition to the bubonic infection, others point to additional
septicemic and
pneumonic forms of plague, which lengthen the duration of outbreaks throughout the seasons and help account for its high mortality rate and additional recorded symptoms. In 2014,
Public Health England announced the results of an examination of 25 bodies exhumed in the
Clerkenwell area of London, as well as of wills registered in London during the period, which supported the pneumonic hypothesis. By the early 14th century, so much filth had collected inside urban Europe that French and Italian cities were naming streets after human waste. In medieval Paris, several street names were inspired by , the French word for "shit". There were and —as well as a . Pigs, cattle, chickens, geese, goats and horses roamed the streets of medieval London and Paris. Medieval homeowners were supposed to police their housefronts, including removing animal dung, but most urbanites were careless. William E. Cosner, a resident of the London suburb of Farringdon Without, received a complaint alleging that "men could not pass [by his house] for the stink [of] ... horse dung and horse piss." One irate Londoner complained that the runoff from the local slaughterhouse had made his garden "stinking and putrid", while another charged that the blood from slain animals flooded nearby streets and lanes, "making a foul corruption and abominable sight to all dwelling near." In much of medieval Europe, sanitation legislation consisted of an ordinance requiring homeowners to shout, "Look out below!" three times before dumping a full chamber pot into the street.
Territorial origins According to a team of
medical geneticists led by
Mark Achtman,
Yersinia pestis "evolved in or near China" over 2,600 years ago. Later research by a team led by Galina Eroshenko placed its origins more specifically in the
Tian Shan mountains on the border between
Kyrgyzstan and China. However more recent research notes that the previous sampling contained East Asian bias and that sampling since then has discovered strains of
Y. pestis in the Caucasus region previously thought to be restricted to China. There is also no physical or specific textual evidence of the Black Death in 14th century China. As a result, China's place in the sequence of the plague's spread is still debated to this day. According to Charles Creighton, records of epidemics in 14th-century China suggest nothing more than typhus and major Chinese outbreaks of epidemic disease post-date the European epidemic by several years. The earliest Chinese descriptions of the bubonic plague do not appear until the 1640s.
Nestorian gravesites dating from 1338 to 1339 near
Issyk-Kul have inscriptions referring to plague, which has led some historians and
epidemiologists to think they mark the outbreak of the
epidemic; this is supported by recent direct findings of
Y. pestis DNA in teeth samples from graves in the area with inscriptions referring to "pestilence" as the cause of death. According to John Norris, evidence from Issyk-Kul indicates a small sporadic outbreak characteristic of transmission from rodents to humans with no wide-scale effect. According to Achtman, the dating of the plague suggests that it was not carried along the
Silk Road, and its widespread appearance in that region probably postdates the European outbreak. As the disease took hold, Genoese traders fled across the
Black Sea to
Constantinople, where the disease first arrived in Europe in summer 1347. The epidemic there killed the 13-year-old son of the
Byzantine emperor,
John VI Kantakouzenos, who wrote a description of the disease modelled on
Thucydides's account of the 5th century BCE
Plague of Athens, noting the spread of the Black Death by ship between maritime cities. the disease spread rapidly all over the island. Galleys from Kaffa reached Genoa and Venice in January 1348, but it was the outbreak in
Pisa a few weeks later that was the entry point into northern Italy. Towards the end of January, one of the galleys expelled from Italy arrived in
Marseilles.
From Italy, the disease spread northwest across Europe,
striking France,
Spain, Portugal, and
England by June 1348, then spreading east and north
through Germany, Scotland and Scandinavia from 1348 to 1350. It was introduced
into Norway in 1349 when a ship landed at
Askøy, then spread to Bjørgvin (modern
Bergen). Finally, it
spread to northern Russia in 1352 and reached
Moscow in 1353. Plague was less common in parts of Europe with less-established trade relations, including the majority of the
Basque Country, isolated parts of Belgium and
the Netherlands, and isolated Alpine villages throughout the continent. According to some epidemiologists, periods of unfavorable weather decimated plague-infected rodent populations, forcing their fleas onto alternative hosts, inducing plague outbreaks which often peaked in the hot summers of the Mediterranean and during the cool autumn months of the southern
Baltic region. Among many other culprits of plague contagiousness, pre-existing malnutrition weakened the immune response, contributing to an immense decline in European population.
West Asian and North African outbreak The disease struck various regions in the Middle East and North Africa during the
pandemic, leading to serious depopulation and permanent change in both economic and social structures. By autumn 1347, plague had reached
Alexandria in Egypt, transmitted by sea from
Constantinople via a single merchant ship carrying slaves. By late summer 1348, it reached
Cairo, capital of the
Mamluk Sultanate, cultural center of the
Islamic world, and the largest city in the
Mediterranean Basin; the
Bahriyya child sultan
an-Nasir Hasan fled and more than a third of the 600,000 residents died. The
Nile was choked with corpses despite Cairo having a medieval hospital, the late 13th-century
bimaristan of the
Qalawun complex. Within two years, the plague had spread throughout the Islamic world, from Arabia across North Africa. The pandemic spread westwards from Alexandria along the African coast, while in April 1348
Tunis was infected by ship from Sicily. Tunis was then under attack by an army from Morocco; this army dispersed in 1348 and brought the contagion with them to Morocco, whose epidemic may also have been seeded from the Islamic city of
Almería in
al-Andalus. During 1349, records show the city of
Mosul suffered a massive epidemic, and the city of
Baghdad experienced a second round of the disease.
Signs and symptoms gangrene of the
fingers due to
bubonic plague causes the skin and
flesh to
die and turn black on the upper thigh of a person infected with bubonic plague. Swollen
lymph nodes (
buboes) often occur in the neck, armpit and groin (
inguinal) regions of plague victims.
Bubonic plague Symptoms of the plague include fever of , headaches,
painful aching joints,
nausea and vomiting, and a general feeling of
malaise. Left untreated, 80% of victims die within eight days. Contemporary accounts of the pandemic are varied and often imprecise. The most commonly noted symptom was the appearance of
buboes (or
gavocciolos) in the groin, neck and armpits, which oozed pus and bled when opened. which may have been caused by
flea-bites, were identified as another potential sign of plague.
Pneumonic plague Lodewijk Heyligen, whose master Cardinal
Giovanni Colonna died of plague in 1348, noted a distinct form of the disease,
pneumonic plague, that infected the lungs and led to respiratory problems. Some estimate that it may have killed between 75,000,000 and 200,000,000 people in
Eurasia. A study published in 2022 of pollen samples across Europe from 1250 to 1450 was used to estimate changes in agricultural output before and after the Black Death. The authors found great variability in different regions, with evidence for high mortality in areas of Scandinavia, France, western Germany, Greece, and central Italy, but uninterrupted agricultural growth in central and eastern Europe, Iberia, and Ireland. The authors concluded that "the pandemic was immensely destructive in some areas, but in others it had a far lighter touch ... [the study methodology] invalidates histories of the Black Death that assume
Y. pestis was uniformly prevalent, or nearly so, across Europe and that the pandemic had a devastating demographic impact everywhere." The Black Death killed, by various estimations, from 25 to 60% of Europe's population. Robert Gottfried writes that as early as 1351, "agents for
Pope Clement VI calculated the number of dead in Christian Europe at 23,840,000. With a preplague population of about 75 million, Clement's figure accounts for mortality of 31%-a rate about midway between the 50% mortality estimated for East Anglia, Tuscany, and parts of Scandinavia, and the less-than-15% morbidity for Bohemia and Galicia. And it is unerringly close to Froissart's claim that "a third of the world died," a measurement probably drawn from St. John's figure of mortality from plague in the
Book of Revelation, a favorite medieval source of information."
Ole J. Benedictow proposes 60% mortality rate for Europe as a whole based on available data, with up to 80% based on poor nutritional conditions in the 14th century. The mass burial sites that have been excavated have allowed archaeologists to continue interpreting and defining the biological, sociological, historical, and anthropological implications of the Black Death. In 1348, the disease spread so rapidly that nearly a third of the European population perished before any physicians or government authorities had time to reflect upon its origins. In crowded cities, it was not uncommon for as much as 50% of the population to die. Half of Paris's population of 100,000 people died. In Italy, the population of
Florence was reduced from between 110,000 and 120,000 inhabitants in 1338 to 50,000 in 1351. At least 60% of the population of
Hamburg and
Bremen perished, and a similar percentage of Londoners may have died from the disease as well, leaving a death toll of approximately 62,000 between 1346 and 1353. Florence's tax records suggest that 80% of the city's population died within four months in 1348. Before 1350, there were about 170,000 settlements in Germany, and this was reduced by nearly 40,000 by 1450. The disease bypassed some areas, with the most isolated areas being less vulnerable to
contagion. Plague did not appear in
Flanders until the turn of the 15th century, and the impact was less severe on the populations of
Hainaut,
Finland, northern Germany, and areas of Poland. Monks, nuns, and priests were especially hard-hit since they cared for people ill with the plague. The level of mortality in the rest of Eastern Europe was likely similar to that of Western Europe in the first outbreak, with descriptions suggesting a similar effect on Russian towns, and the cycles of plague in Russia being roughly equivalent. In the first outbreak, two thirds of the population contracted the illness and most patients died; in the next, half the population became ill but only some died; by the third, a tenth were affected and many survived; while by the fourth occurrence, only one in twenty people were sickened and most of them survived. The Black Death killed about 40% of Egypt's population. In Cairo, with a population numbering as many as 600,000, and possibly the largest city west of China, between one third and 40% of the inhabitants died within eight months. But along with population decline from the pandemic, wages soared in response to a subsequent labour shortage. In some places rents collapsed (e.g., lettings "used to bring in £5, and now but £1.") Taxes and tithes became difficult to collect, with living poor refusing to cover the share of the rich deceased, because many properties were empty and unfarmed, and because tax-collectors, where they could be employed, refused to go to plague spots.
Environmental A study performed by Thomas Van Hoof of the Utrecht University suggests that the innumerable deaths brought on by the pandemic cooled the climate by freeing up land and triggering
reforestation. This may have led to the
Little Ice Age.
Persecutions in 1349. Miniature from a 14th-century manuscript
Antiquitates Flandriae by
Gilles Li Muisis Renewed religious fervor and
fanaticism increased in the wake of the Black Death. Some Europeans targeted "various groups such as
Jews,
friars, foreigners, beggars,
pilgrims", lepers, and
Romani, blaming them for the crisis.
Lepers, and others with skin diseases such as
acne or
psoriasis, were killed throughout Europe. Because 14th-century healers and governments were at a loss to explain or stop the disease, Europeans turned to
astrological forces, earthquakes and the
poisoning of wells by Jews as possible reasons for outbreaks. Many believed the epidemic was a
punishment by God for their sins, and could be relieved by winning
God's forgiveness. There were many attacks against Jewish communities. In the
Strasbourg massacre of February 1349, about 2,000 Jews were murdered. During this period many Jews relocated to
Poland, where they received a welcome from King
Casimir the Great.
Social 's
The Triumph of Death reflects the social upheaval and terror that followed the plague, which devastated medieval Europe. One theory that has been advanced is that the Black Death's devastation of
Florence, between 1348 and 1350, resulted in a shift in the world view of people in 14th-century Italy that ultimately led to the
Renaissance. Italy was particularly badly hit by the pandemic, and the resulting familiarity with death may have caused thinkers to dwell more on their lives on Earth, rather than on
spirituality and the
afterlife. It has also been argued that the Black Death prompted a new wave of piety, manifested in the
sponsorship of religious works of art. This does not fully explain why the Renaissance occurred in Italy in the 14th century; the Renaissance's emergence was most likely the result of the complex interaction of the above factors, in combination with an
influx of Greek scholars after the
fall of the Byzantine Empire. As a result of the drastic reduction in the populace the value of the working class increased, and commoners came to enjoy more freedom. To answer the increased need for labour, workers travelled in search of the most favorable position economically. Prior to the emergence of the Black Death, the continent was considered a feudalistic society, composed of
fiefs and city-states frequently managed by the Catholic Church. The pandemic completely restructured both religion and political forces; survivors began to turn to other forms of spirituality and the power dynamics of the fiefs and city-states crumbled. The word "
quarantine" has its roots in this period, though the practice of isolating people to prevent the spread of disease is older. In the city-state of
Ragusa (modern
Dubrovnik, Croatia), a thirty-day isolation period was implemented in 1377 for new arrivals to the city from plague-affected areas. The isolation period was later extended to forty days, and given the name "quarantino" from the Italian word for "forty". All institutions were affected. Smaller monasteries and convents became unviable and closed. Up to half parish churches lost their priest, apart from the parishioners. Religious sensibilities changed: ==Recurrences==