The Medieval Understanding of the Black Plague

This is an essay I wrote for my class on the history of medicine. It provides a window on the fascinating world of medieval thought. While it has a strongly academic flavor, I think it avoids being dense. If you’re doing undergraduate world on the Plague you may find it useful for its use of many of the available primary sources. The numbers in brackets refer to the notes below the text.

The most devastating outbreak of the Black Plague struck Europe from 1347 to 1350 and is estimated to have killed between thirty and fifty percent of the population.[1] Modern science reveals that the plague was caused primarily by bubonic plague spread through fleas carried on rats. A pneumonic form of the plague that could be spread between humans also existed, and some historians believe that other diseases such as anthrax may have operated in conjunction with bubonic plague.[2] Lacking this scientific understanding, medieval Europeans turned to religion, astrological and humoral theories, and allegations of conspiracy to explain the devastation that consumed their world. While largely ineffective in preventing or treating the plague, these ideas probably did provide some comfort and even some sense of control by attempting to pull the plague out of the dark realm of the unknown. Medieval theories and beliefs concerning the plague’s causes provide a window into the understanding of disease, medicine, and the wider world during the Middle Ages.

Christianity was one of the most dominant forces in medieval Europe. After the fall of Rome, the church emerged as a powerful stabilizing institution. William Zouche, the Archbishop of York, wrote in 1348 that the plague was “surely caused by the sins of men who, while enjoying good times, forget that such things are the gifts of the most high giver.”[3] To Zouche, it was evident that such a devastating plague could only be the work of God against unrepentant sinners. The “only hope” he wrote, was through “orisons and prayers,” to convince God “to turn away this anger.”[4] Zouche commanded that processions be held every Wednesday and Friday in every church, from the cathedral to the lowly parishes, and that special prayers be said daily.[5] Upon hearing news of the plague’s arrival in a “neighboring kingdom” from the east, Ralph of Shrewsbury, the Bishop of Bath and Wells, urged his fellow clergy to pray “devoutly and incessantly,” to prevent “a similar pestilence [from] stretch[ing] its poisonous branches into this realm.”[6] The writings of Zouche and Ralph reveal a view of the world in which God takes an active role in the affairs of humans, and their spiritual activities have consequences not only after death, but in the world around them.

Despite their best efforts, prayer did not halt the advance of the plague into England. In 1349, King Edward III sent a letter to the bishops of his kingdom.[7] He blamed the people for the spread of the plague, because instead of humbling themselves before God, their “sinfulness and pride [were] constantly increasing.”[8] Among the survivors of the plague, Edward noted that “charity has grown more than usually cold.”[9] This condemnation may in part refer to victims of the plague who were abandoned by the healthy who feared contact with the infected. Edward believed the plague had its origins in divine retribution, and feared that such practices would provoke God further, leading to a “much greater calamity.”[10] He continued to urge prayer and religious devotion “so that merciful God might repel the plague and illness and confer peace and tranquility.”[11] Edward was certain that by driving out “spiritual wickedness” from the people, the “malignancy of the air and other elements will also depart.”[12] Edward’s writings affirm the intimate connection between the spiritual and physical worlds in the medieval mind. Wickedness of the spirit, in Edward’s eyes, manifested itself in the bodily corruption of the plague. Only by purifying the soul could they hope to maintain the health of the body.

As the plague was generally considered to be divine punishment, there was a great deal of discussion about the particular sins that had invoked God’s wrath. An anonymously written poem from the fourteenth century lamented that “vices rule unchallenged,” and “[n]o one thinks on the crucified Christ.”[13] The author believed that the victims of plague suffered and died “as a token of vengeance” for their sins.[14] He lays out a vision of a society which had become corrupt to the core. “[P]eace and patience are thoroughly plundered,” he writes, and “love and justice are not at home.”[15] A great deal of abdication of responsibility and abuse of power are recounted. The poet laments that “the sloth of the shepherds leaves the flocks straying,” and “the poor suffer through the depravity of the rich.”[16] Rater than wisdom, this writer sees that “[r]ulers are moved by favour.”[17] In a treatise on the Ten Commandments from the 1360s, the author argues that children of the day did not properly respect their parents, and asserts that “it is in vengeance of this sin of dishonouring and despising fathers and mothers that God is slaying children by pestilence.”[18] Facing the plague, chroniclers of the period turned their sights to the problems of society to explain why such incomprehensible suffering could occur.

In 1355, Heinrich von Herford placed the blame for the plague on the deplorable state of the clergy.[19] He wrote that “the heresy of simony grew so strong among the clergy, and overwhelmed them so completely, that everyone … in some fashion openly bought and sold spiritualities of all sorts.”[20] The selling of religious positions had grown so common place, according to Herford, that the perpetrators not only went unpunished, but even without shame or remorse.[21] Herford reports that aside from positions in the church, actual church buildings and objects such as alters were traded for “money, women and sometimes concubines.”[22] Worse still, members of the clergy gambled with these possessions. He writes that that they “staked them, lost and won them, on a game of dice.”[23] The purchasing of positions led to “foul tempered, illiterate, underage, inexperienced, [and] stupid” people in all levels of the church.[24] If one wanted to trace the source of the plague, Herford believed they need look no further than “their careers and their doctrine.”[25] As God’s representatives and highest servants on earth, the clergy had a sacred responsibility to lead virtuous lives. All around him, Herford was dismayed to find examples of this trust being betrayed. Surely, if the most holy among them had fallen into such deep sin, they could only expect disaster.

New fashions in clothing were also cited as a source of divine displeasure. Henry Knighton recounted that, during tournaments, “a troop of ladies would turn up dressed in a variety of extraordinary male clothing, as if taking part in a play.”[26] He saw these women as “deaf to the demands of modesty,” and inviting the wrath of God.[27] In 1344, an anonymous monk recounted that, for about eighteen years, the “English have been madly following outlandish ways, changing their grotesque fashions of clothing yearly.”[28] They abandoned the “decent style of long, full garments for clothes which are short, tight, impractical, slashed, every part laced, strapped, or buttoned up, with the sleeves of the gowns and the tippets of the hoods handing down to absurd lengths.”[29] This monk was so shocked by the new fashions that he believed those who wore the new clothes looked “more like torturers, or even demons, than men.”[30] The monk was certain that the “sin of pride” represented by the new fashions would “bring misfortune in the future.”[31] After the 1348 outbreak, John of Reading saw the plague as this misfortune.[32] John claimed that the new styles of clothes were so tight that they “did not allow them to kneel before God or to the saints.”[33] Searching for a reason for the plague, writers latched on to changes they saw as destructive to society. In the religious atmosphere of the Middle Ages, with its close association between the material and spiritual worlds, it was not at all strange that any alteration in the highly ordered world could manifest itself in a calamity such as the plague

The belief in the plague as an expression of God’s anger gave rise to the Flagellant movement. A chronicler writing in 1349 explained that the Flagellants took their name from “whips [flagella] which they used in performing the public penance.”[34] Flagellants roamed throughout Europe, assembled in towns, and collectively whipped themselves to atone for the sins they believed had summoned the plague. Although the Flagellant movement began with papal support, it eventually spiraled out of the church’s control and came to be seen as subversive.[35] After Pope Clement VI threatened the Flagellants with excommunication, other religious and secular leaders took action against Flagellants which included public beatings and occasionally executions. The extremism of this movement indicates the desperation felt by those who lived through the plague, and the depth to which they believed in the religious explanation of its origin.

In 1348 the Paris medical establishment put together a report on the plague.[36] These physicians maintained that God was the ultimate cause of the plague, but attempted to explain the physical mechanisms through which it operated.[37] The report was supposed to have drawn from the “opinions of the most brilliant ancient philosophers and modern experts, astronomers as well as doctors of medicine.”[38] By the time of the plague, the Hippocratic-Galenic tradition of medicine had been reintroduced into Europe, and this understanding is infused with astrological theories throughout the report. The Hippocratics theorized that the body was composed of four humors, each of which represented one of the four elements. Health resulted from proper balancing of these humors, and disease was caused by imbalance. In the Paris report as well as other medically focused documents, medieval physicians spent most of their time explaining the causes of this imbalance and how to avoid them.

The report asserted that multiple causes combined to bring about the great mortality of the plague. The first of these causes was the configuration of the planets. The blame is specifically laid on an astrological event that occurred in 1345.[39] They wrote that “[i]n 1345, at one hour after noon on 20 March, there was a major conjunction of three planets in Aquarius.”[40] This distant event caused “a deadly corruption of the air.”[41] As evidence for this causal connection, the report cited Albertus Magnus, who wrote that a “conjunction of Mars and Jupiter causes a great pestilence in the air.”[42] Even as the physicians in Paris attempted to attribute the plague to natural processes, their explanation was built upon the examination of distant and unalterable astrological phenomenon. It is permeated with a sense that humans are subject to forces of the natural world over which they have no control.

The Paris staff also examined unusual geological events and changes in climatic patterns. Noting that an earthquake had recently occurred, the physicians posited that “the escape of rottenness” from the earth during the quake contributed to the plague.[43] They noted that “the ancients, most notably Hippocrates, are agreed that if the four seasons run awry, and do not keep their proper course, then plagues and mortal passions are engendered that year.”[44] In Hippocratic medicine, it was believed that the weather could cause the four humors within the body to become imbalanced and lead to disease. The Paris physicians went on to record that the “seasons have not succeeded each other in the proper way.”[45] In their attempt to rationalize the devastation of the plague, the physicians invoked anomalies ranging from the astrological conjunction to earthquakes and changes in the weather pattern. Each of these factors was cast within the framework of the Hippocratic-Galenic tradition, and together they formed a more or less logically consistent explanation of the inexplicable mortality.

While environmental factors were vital to the Paris physicians’ understanding of the plague’s causes, they also discussed why some people got sick and others remained healthy. They wrote that “no cause is likely to have an effect unless the patient is susceptible to its effects” (163). Any activity that made the body “hot or moist” was suspected.[46] They specifically cited “too much exercise, sex and bathing” as dangerous.[47] Interestingly, “persistent worriers” were identified at higher risk, and “babies, women, and young people” were also believed to be more susceptible to the plague.[48] Even the more secular theories of the plague did not escape religious and social sentiments. The persistent worriers may have been identified as unhealthy not because their activity caused stress or other physiological reactions about which medieval medicine had no knowledge, but because worrying revealed a lack of faith in God to provide for the future. The other populations at heightened risk, children and women, were viewed as weaker than and subordinate to men in the Middle Ages.

Strangely, the Paris document did not lay out any dietary recommendations, the cornerstone of Hippocratic treatment. In his 1365 treatise on the plague, John of Burgundy asserted that the cause of “the mortality is not only the corruption of the air, but the abundance of corrupt humours within those who die of the disease.”[49] Although he accepted the idea that the air had been corrupted, John placed more of an emphasis on the factors that made individuals susceptible to the plague. He believed that people should “avoid over-indulgence in food and drink, and also avoid baths and everything which might rarefy the body and open the pours, for the pours are the doorways through which poisonous air can enter.”[50] John suggested eating “little or no fruit,” and “season[ing] food with strong vinegar.”[51] By keeping the proper balance of humors and avoiding dangerous activities, John proposed it was possible to reduce the risk of falling ill from the influence of the corrupted air.

In 1364 John Sacobus wrote about avoiding the plague. Sacobus began by suggesting that the reader should “meekly confess his sins, for it is the highest remedy in time of pestilence.”[52] Clearly Sacobus believed that God had the power to heal and protect from the plague, but he also provided more secular advice. He recommended avoiding every kind of “purification and stinking,” among which he included “fleshly lust with women.”[53] Sacobus advocated the use of herbs such as leaves of bay tree, juniper, and wormwood so that the bad air can be “made feeble.”[54] This suggests the idea that corrupted air could be purified, or at least repelled, by pure air. Indicating the concept of contagion, Sacobus warned against common baths and suggested avoiding people in general.[55] Like John of Burgundy, Sacobus recommended using plenty of vinegar in food because “all sour things stop the way of humours and suffer no venomous things to enter into a man’s body.”[56] Sacobus confidently asserted that the validity of his advice was proven by his own health.

Written a generation after the 1348 outbreak of plague, one treatise argued against the astrological explanation of the plague.[57] The author maintained that such an astrological event would affect all people equally. He seemed to dismiss the idea that individual susceptibility played a role in determining who became sick. This author’s explanation rested on the “corrupt and poisonous earthy exhalation[s]” released during earthquakes.[58] He attempted to prove that air within the earth is corrupted by recalling that men who enter previously sealed wells were sometimes asphyxiated.[59] He also points to the occurrence of an earthquake shortly before the plague began in Germany.[60] He did nothing, however, to address the same kind of criticism he laid against the astrologers: why the air corrupted by earthquakes, which presumably would be dispersed evenly, affected different people in different ways.

The ordinances enacted by cities in their efforts to prevent the spread of the plague also illustrate how it was understood. Examples of such ordinances exist from the city of Pistoia, Italy in the year 1348.[61] The regulations begin by declaring that no one “shall dare presume to go to Pisa or Lucca; and no one shall come to Pistoia from those places” without being granted special permission.[62] This quarantine tactic is just about the only prevention strategy of medieval medicine that modern science would deem at all effective against the plague. Several rules deal with the theory that infected corpses could corrupt the air. They required that bodies remain within their homes until “they have been enclosed in a wooden box, and the lid of planks nailed down so that no stench can escape.”[63] Similarly, graves were to be dug sufficiently deep “to avoid the foul stench which comes from dead bodies.”[64] To combat the dangers of corrupted food, numerous regulations were set out for the proper processing of meats.[65] The regulations of Pistoia reveal that though they may have misunderstood the mechanism of disease, medieval officials recognized the reality of contagion. Such regulations subtly reject the idea of the plague as divine punishment, for the will of God certainly could not have been thwarted by a city council. It also seems to deny the theory of air universally corrupted by a distant astrological event. These practical regulations, which were set out with no intention of explaining or theorizing on the origins of the plague, have turned out to provide the most practical medieval understanding of the plague.

The most sinister medieval theory of the plague’s origins is the idea that it was intentionally introduced through a Jewish conspiracy intended to exterminate the Christians. A Franciscan friar recorded in 1349 that some believed “the Jews planned to wipe out all the Christians with poisoned wells and springs everywhere.”[66] Indicating the sophistication of the medieval justice system, the friar confidently wrote that “many Jews confessed as much under torture.”[67] To escape the torment of medieval torture, Jews claimed they had “bred spiders and toads in pots and pans, and had obtained poison from overseas.”[68] The friar went on to claim that “bags full of poison” were found in wells and springs where the plague had occurred.[69] The Castellan of Chillon also discussed confessions obtained through torture. He wrote that a Jewish prisoner recalled the “Rabbi Jacob” sending him a poisonous powder with a letter demanding he poison the wells on threat of excommunication.[70] The man went on to confess that “one evening he secretly put the poisonous powder under a stone in a spring.”[71] The man also claimed that similar instructions were give to other Jews, suggesting a large conspiracy. Like the religious arguments about the plague, belief in the Jewish conspiracy sprung from a desire to assign blame for the devastating pestilence. Rather than believing that it was God’s just punishment for the sins of the Christians, advocates of the Jewish conspiracy placed the responsibility for the plague on the devious designs of an unfamiliar group. The lack of an adequate scientific understanding of the plague in this instance fueled a practice that only added to the human suffering of the plague years.

Although the belief in the Jewish conspiracy was wide spread, it also had significant opposition. The “justices, officials, and councilors of Cologne” compiled a letter to the people of Strassburg stating that they were “of the opinion that this mortality and its attendant circumstances are caused by divine vengeance and nothing else.”[72] They forbid “any harassment of the Jews in our city because of these flying rumors.”[73] Pope Clement VI also stood against the accusations. He wrote that “it cannot be true that the Jews, by such heinous crime, are the cause or occasion of the plague.”[74] Although there would be no punishment terrible enough if the conspiracy were found to be true, Clement argued that “throughout many parts of the world the plague, by the hidden judgment of God, has afflicted and afflicts the Jews and many other races who never lived alongside them.”[75] In Clement VI’s mind the plague was undoubtedly the work of God, not a widespread and virtually impossible act of conspiracy.

The medieval understanding of the Black Plague offers a window into the religious, medical, and social beliefs of the Middle Ages. It was almost universally believed that God was the source of the plague, and that it was intended as punishment for the sins of humanity. Some used astrology and the tools of medicine inherited from the ancient world to understand the physical mechanisms of the plague’s origin and spread. Out of a mixture of anxiety and prejudice, Jews became the scapegoat for some who alleged the plague was the result of a grand conspiracy. The writings that survive allow one to peer into that distant society at its greatest moment of crisis and discover how the people who lived through the disaster used the framework of medieval beliefs and social structures to comprehend the devastation they saw unfolding around them.


1 Cantor, Norman F., In the Wake of the Plague (New York: Simon & Schuster, 2001), 7.

2 Cantor, Norman F., 13-16.

3 Zouche, William, “Intercessionary processions (1),” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 111.

4 Zouche, 111.

5 Zouche, 111.

6 Ralph of Shrewsbury, “Intercessionary processions (2),” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 112.

7 Edward III, “Edward III to the bishops, 5 September 1349,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 117.

8 Edward III, 117.

9 Edward III, 117.

10 Edward III, 118.

11 Edward III, 118.

12 Edward III, 118.

13 “The sins of the times,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 126.

14 “The sins of the times,” 126.

15 “The sins of the times,” 126.

16 “The sins of the times,” 126.

17 “The sins of the times,” 126.

18 “The disobedience of children,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 134.

19 Herford, Heinrich von, “The failings of the clergy,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 127.

20 Herford, Heinrich von, 128.

21 Herford, Heinrich von, 128.

22 Herford, Heinrich von, 128.

23 Herford, Heinrich von, 128.

24 Herford, Heinrich von, 128.

25 Herford, Heinrich von, 128.

26 Knighton, Henry, “Divine disapproval of tournaments,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 130.

27 Knighton, Henry, 130.

28 “Indecent clothing as a cause of the 1348-49 epidemic,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 131.

29 “Indecent clothing as a cause of the 1348-49 epidemic,” 131.

30 “Indecent clothing as a cause of the 1348-49 epidemic,” 131.

31 “Indecent clothing as a cause of the 1348-49 epidemic,” 131.

32 “Indecent clothing as a cause of the 1348-49 epidemic,” 131.

33 John of Reading, “Indecent clothing as a cause of later outbreaks,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 134.

34 “The flagellants,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 150.

35 Ziegler, Phillip, The Black Death (New York: John Day Company, 1969), 95.

36 “The report of the Paris medical faculty, October 1348,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 158-163.

37 “The report of the Paris medical faculty, October 1348,” 163.

38 “The report of the Paris medical faculty, October 1348,” 158.

39 “The report of the Paris medical faculty, October 1348,” 159.

40 “The report of the Paris medical faculty, October 1348,” 159.

41 “The report of the Paris medical faculty, October 1348,” 159.

42 “The report of the Paris medical faculty, October 1348,” 159.

43 “The report of the Paris medical faculty, October 1348,” 161.

44 “The report of the Paris medical faculty, October 1348,” 161.

45 “The report of the Paris medical faculty, October 1348,” 161.

46 “The report of the Paris medical faculty, October 1348,” 163.

47 “The report of the Paris medical faculty, October 1348,” 163.

48 “The report of the Paris medical faculty, October 1348,” 163.

49 John of Burgundy, “The treatise of John of Burgundy,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 185.

50 John of Burgundy, 186.

51 John of Burgundy, 186.

52 Jacobus, John, “The dangers of corrupted air,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 176.

53 Jacobus, John, 176.

54 Jacobus, John, 176.

55 Jacobus, John, 177.

56 Jacobus, John, 177.

57 “Earthquakes as the cause of plague,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 177.

58 “Earthquakes as the cause of plague,” 178.

59 “Earthquakes as the cause of plague,” 178.

60 “Earthquakes as the cause of plague,” 178.

61 “Ordinances against the spread of plague, Pistoia, 1348,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 194.

62 “Ordinances against the spread of plague, Pistoia, 1348,” 195.

63 “Ordinances against the spread of plague, Pistoia, 1348,” 195.

64 “Ordinances against the spread of plague, Pistoia, 1348,” 196.

65 “Ordinances against the spread of plague, Pistoia, 1348,” 198-199.

66 Gigas, Herman, “Well-poisoning,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 207.

67 Gigas, Herman, 207.

68 Gigas, Herman, 207.

69 Gigas, Herman, 207.

70 “Examination of the Jews captured in Savoy,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 212.

71 “Examination of the Jews captured in Savoy,” 212.

72 “Letter from Cologne to Strassburg,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 220.

73 “Letter from Cologne to Strassburg,” 220.

74 Clement VI, “Mandate of Clement VI concerning the Jews,” in The Black Death, trans & ed. Rosemary Horrox (New York: Manchester University Press, 1994), 222.

75 Clement VI, 222.

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