Why did the plague return in waves?
The Black Death of 1347–1351 is the most studied pandemic in pre-modern history, but it is only the first chapter in a longer story. The plague did not arrive in 1347, sweep across Europe, and then disappear. It returned, in waves, throughout the late medieval and early modern periods, and the recurrences were, in some ways, more important than the original pandemic in shaping European life. The pattern of recurrence, the factors that produced it, and the demographic and economic effects of the recurring waves are the subject of this article.
The wider context is set out in Recurring plagues and their decline and in the overview of the Black Death. The eventual disappearance of plague is treated in How Europe finally escaped the cycle of plague. The saints and folk beliefs of the period are surveyed in Late medieval plague saints and folk beliefs. The medical response, which changed markedly over the four centuries of recurring outbreaks, is examined in Medieval medical responses to the Black Death.
The Pestis Secunda and the Children
The first major recurrence of the plague, the Pestis Secunda or “Second Plague,” swept across Europe in 1361–1362. The outbreak is recorded in a number of contemporary chronicles, including the Chronicon Henrici Knighton, the canon of Leicester who recorded the events of the 1360s in his chronicle. Knighton, who had been an eyewitness to the original Black Death in 1349, noted that the Pestis Secunda attacked “those who were young and not yet grown up, and others who had not had the disease before.” The chronicler Henry of Reading, in a similar passage, reported that the mortality of the children “was so great that scarcely one in twenty survived.”
The Pestis Secunda was, in demographic terms, a particularly significant outbreak. The mortality was lower than in 1347–1351 — perhaps 10% to 20% of the population, compared with 30% to 60% in the original pandemic — but the demographic effect was concentrated in the children. The first cohort of children born after the Black Death had not been exposed to the original disease in infancy, and they had therefore no acquired immunity. The mortality among them was correspondingly high. The effect of the Pestis Secunda was therefore to deprive the European population of the children of the late 1340s, and to delay the demographic recovery of the continent by a generation.
The Pestis Secunda was followed by further outbreaks in 1369, 1375, 1382, 1390, and roughly every five to twelve years thereafter. The pattern was not regular, and the severity of the outbreaks varied widely. Some years — 1349, 1361, 1400, 1439, 1471, 1563, 1593, 1630, 1665, 1720 — saw particularly severe outbreaks that affected large parts of the continent. Other years saw only localized outbreaks, often in port cities or in areas where the disease had not been present for some time. The pattern of recurrence was, in this sense, an irregular pattern of regional and continental outbreaks, with no single rhythm.
A Catalogue of Outbreaks
Several major outbreaks stand out in the history of recurring plague in Europe. The Pestis Tertia of 1375 affected much of Europe, including England, France, and Italy, with mortality rates comparable to those of the Pestis Secunda. The outbreak of 1400 in northern Italy and southern France was associated with the famine and bad harvests of the late 1390s. The outbreak of 1439–1440 in northern Italy and the Low Countries was one of the most severe of the fifteenth century, and it was recorded in the chronicle of the Milanese physician Gian Galeazzo Visconti.
The outbreak of 1563–1564 was particularly severe in the Low Countries, in England, and in Spain. The mortality in London was unusually high, and the London bills of mortality recorded a death rate of over 25% in some parishes. The outbreak of 1575–1577 in northern Italy — the great plague of Milan, Venice, and Verona — was one of the most thoroughly documented outbreaks of the sixteenth century, and the response of the Milanese magistrato di sanità became a model for the public health systems of the early modern period.
The outbreak of 1593 in London was severe but localised, and the city bills of mortality recorded a death rate of about 11%. The outbreak of 1629–1631 in northern Italy — the great plague of Milan — was associated with the Thirty Years’ War and the famine that followed, and the mortality was over 50% in some parts of the city. The outbreak of 1630–1631 in Venice, associated with the famous carnival of 1630, is the subject of one of the great plague narratives of the early modern period, the Storia della guerra di Castro of Alessandro Manzoni (1827), although Manzoni’s account is set in Milan.
The Great Plague of London of 1665 is the most thoroughly documented outbreak of plague in English history. The mortality is usually estimated at 100,000, or roughly a quarter of the population of the city. The outbreak is known in detail because of the parish records, the bills of mortality, and the diary of Samuel Pepys. The outbreak was eventually contained by the Great Fire of London of September 1666, which destroyed much of the rat-infested timber housing of the medieval city.
The Great Plague of Marseilles of 1720 was, as we have seen, the last major outbreak of plague in Western Europe. After Marseilles, the great European outbreaks of plague came to an end. The last outbreak in the British Isles was the small outbreak in Noja, in southern Italy, in 1815. The last outbreak in the Mediterranean was the outbreak in Porto, in 1899.
Why Plague Never Really Left
The most important reason for the recurring outbreaks is that the plague never really left Europe between 1347 and the early eighteenth century. The disease persisted, in low levels, in the rodent population of the great commercial ports and the grain-growing regions of the European plain, and it flared up periodically into epidemics when conditions were favourable. The persistence of the disease in the rodent population has been documented by the work of the paleoclimatologist Jean-Noël Biraben, by the historian of medicine Paul Slack, and by the contributors to The Cambridge History of the Black Death (edited by Mark Bailey, 2015).
The mechanism of persistence is now well understood. The Yersinia pestis bacterium circulates in the rodent population, and is transmitted from rodent to rodent by the rat flea. When the rat population is healthy, the bacterium circulates at low levels. When the rat population is stressed — by famine, by cold, by flooding — the rats die, the fleas leave the dead rats and seek new hosts, and the bacterium is transmitted to humans. The cycle is well documented in modern outbreaks, and there is no reason to think that it was not the same in the medieval and early modern periods.
The conditions that favoured an outbreak were therefore the conditions that stressed the rat population and produced a high mortality among rats. The most important of these conditions were the following.
Demographic recovery. When the population began to grow again after a major outbreak, the new generation of children provided a fresh supply of susceptible hosts. The outbreaks of 1361–1362 and 1563, for example, both fell particularly hard on children. The mechanism is the same as the mechanism of the Pestis Secunda: the new generation had not been exposed to the disease in infancy, and it had therefore no acquired immunity.
Climate and weather. The Yersinia pestis bacterium is sensitive to temperature and humidity, and outbreaks were more common in years of mild, wet weather. The cool, damp years of the Little Ice Age, especially in the late sixteenth and early seventeenth centuries, were associated with severe outbreaks. The work of the paleoclimatologists — particularly the work of the contributors to The Cambridge History of the Black Death — has shown that the correlation between climate and outbreak is strong, and that the worst outbreaks of the late medieval and early modern periods were associated with periods of mild, wet weather.
Trade and travel. Outbreaks often followed the trade routes, and the major commercial ports were the first to be affected in any given wave. The great Hanseatic ports, the Italian maritime republics, the great fairs of Champagne, the wool markets of England — all of these were nodes in the network along which the plague travelled. The mechanism is the same as the mechanism of the original Black Death: the rats and the fleas of the medieval ships were the principal vectors of the disease, and the ships themselves were the principal means by which the disease was carried from one port to the next.
Grain and famine. Outbreaks of plague were often associated with bad harvests and famine. The weakened condition of the population, and the movements of people in search of food, helped the disease to spread. The outbreak of 1400 in northern Italy and southern France, for example, was associated with the bad harvests and famine of the late 1390s. The outbreak of 1629–1631 in northern Italy was associated with the famine that followed the Thirty Years’ War.
War. Wars, by disrupting the normal systems of public health and by producing large movements of troops, were also associated with outbreaks of plague. The Thirty Years’ War, for example, was associated with severe outbreaks of plague in Germany in the 1630s and 1640s. The wars of the Italian cities, in the fourteenth and fifteenth centuries, were associated with outbreaks of plague in northern Italy.
A Demographic Regime of High Mortality
The cumulative demographic effect of the recurring outbreaks was, in the long run, more important than the impact of the original Black Death. The repeated waves of plague kept the European population low for centuries, and they prevented the kind of demographic recovery that would otherwise have been expected. The European population, which had been perhaps 70 to 80 million on the eve of the Black Death, did not reach that level again until the early seventeenth century, and it did not exceed it until the eighteenth.
The argument has been most fully developed by the historian David Herlihy, in The Black Death and the Transformation of the West (1997), and by the demographers Josiah Russell and J. C. Russell in their studies of medieval population. Herlihy argued that the recurring outbreaks of plague produced a “demographic regime” of high mortality and slow growth that lasted until the seventeenth or eighteenth century, and that the demographic regime was, in turn, the principal cause of the long-run transformation of the European economy and society. The argument is now widely accepted, although the demographic details remain debated.
The recurring outbreaks also had a profound effect on the age structure of the European population. The repeated loss of young adults and children meant that the surviving population was, on average, older than it would otherwise have been. This had implications for everything from the labour market to the marriage pattern, and it contributed to the long, slow demographic transition of the early modern period. The high age at first marriage, which is one of the distinctive features of the early modern European population, is in part a consequence of the recurring outbreaks of plague.
The Long Shadow
The recurring waves of plague shaped European life for four hundred years, and the long shadow of the disease can be traced in the literature, the art, the religion, the demography, and the politics of the late medieval and early modern world. The memento mori, the Danse Macabre, the transi tomb, the flagellant procession, the plague doctor, the sanità, the quarantine — these institutions and images, which originated in the wake of the original Black Death, became permanent features of European culture, and they have come to stand, in the popular imagination, for the entire age of plague.
The story of the recurring plagues is, in the end, the story of how Europe learned to live with mass death. The catastrophe of 1347–1351 was a turning point, but it was only the first chapter in a longer story. The recurrences of the fifteenth, sixteenth, and seventeenth centuries forced Europeans to develop new medical theories, new public health practices, new religious responses, and new attitudes toward death itself. The decline of the plague in the early eighteenth century was the end of a long historical process, and it is one of the great demographic transitions of European history.
References
- Herlihy, David. The Black Death and the Transformation of the West. Harvard University Press, 1997.
- Bailey, Mark, ed. The Cambridge History of the Black Death. Cambridge University Press, 2015.
- Benedictow, Ole J. Plague in the Late Medieval Nordic Countries: A Historical and Epidemiological Study. Middelalderforlaget, 2012.
- Slack, Paul. The Impact of Plague in Tudor and Stuart England. Routledge & Kegan Paul, 1985.
- Biraben, Jean-Noël. Les hommes et la peste en France et dans les pays européens et méditerranéens. 2 vols. Mouton, 1975–1976.