The great pestilence

What a catastrophe actually caused, and why a famous explanation does not survive comparison

A The pandemic that reached Europe in 1347 killed a proportion of the population that has no modern parallel. Estimates vary by region and by method, but a range between a third and a half of the population of Europe within about four years is accepted by most historians, and some districts lost considerably more. Nothing in the subsequent history of the continent — no war, no famine, no later epidemic — approaches it, and the interesting historical question is not how many died but what a mortality of that magnitude did to the societies that survived it.

B The identity of the disease was settled only recently, and by a method unavailable to historians until this century. Bacterial DNA recovered from the dental pulp of skeletons in plague cemeteries has confirmed the presence of Yersinia pestis in victims across Europe, which closed a long argument in which anthrax, a viral haemorrhagic fever and several other candidates had been proposed. What the genetic evidence has not settled is transmission. The classical account, involving rats and their fleas, fits the biology but struggles with the speed and the seasonal pattern of the medieval spread, and a competing account in which the bacterium passed between people via human fleas and lice accounts for the epidemiology better. The dispute is active and turns on modelling rather than on new excavation.

C The economic consequences are where the argument becomes consequential, because the standard account has become a textbook example of a beneficial catastrophe. In outline it runs as follows. The land of Europe was, before 1347, supporting about as many people as its agriculture could feed; afterwards it was supporting far fewer, so the survivors had more land, more livestock and more capital each. Labour became scarce and therefore expensive, wages rose sharply, rents fell, and the people at the bottom of the hierarchy found themselves, for the first time, in possession of bargaining power.

D The evidence for the wage rise is good. Records from English estates show real wages for agricultural labourers roughly doubling within a few decades, and remaining high for a century and a half. The evidence that the landowners resisted is equally good: legislation was passed within a few years of the pandemic attempting to fix wages at their previous levels and to compel labourers to accept work at those rates. That such laws were passed repeatedly is the strongest evidence that they were not working.

E Where the standard account becomes questionable is in what it concludes from this. The claim that the pandemic ended serfdom in Europe founders on a comparison that is easily made and rarely mentioned: eastern Europe suffered the same mortality and moved in the opposite direction, with landlords tightening obligations and binding peasants more firmly to the land over the following two centuries. The same shock produced emancipation in one half of the continent and its reverse in the other, which means the shock cannot have been the cause. What differed was the balance of power beforehand — the strength of towns, the ability of lords to act collectively, the availability of somewhere else for a labourer to go. Where a peasant could walk to a city and be beyond his lord's reach within a day, scarcity translated into freedom; where the nearest town was small and its rulers were the same men who owned the land, it translated into tighter control.

F A second overstatement concerns technology and enterprise. Expensive labour is often said to have prompted a search for machinery, and there is something in it, but the interval is awkward: the mechanisation usually cited followed four centuries later, in a country whose wages had by then risen for quite different reasons. Historians who argue for the connection are obliged to posit a very long chain of causation, and the chain has weak links at several points. It is more defensible to say that the pandemic altered the conditions under which later developments occurred than that it produced them. The distinction sounds pedantic and is not: one version makes a fourteenth-century epidemic the cause of the modern economy, and the other makes it one of the circumstances that a much later and quite separate set of causes had to work within.

G What the episode illustrates best is a general difficulty with historical explanation. A catastrophe of this scale touches everything, so every subsequent change can be connected to it by a plausible route, and the connections are easy to construct and hard to test. The comparison between eastern and western Europe is valuable precisely because it functions as something rare in history: a natural experiment, in which the same shock was applied to societies whose institutions differed, and produced opposite results. The lesson is not that the pandemic changed nothing. It is that what a shock does depends on what it hits, and that a shock is therefore never a sufficient explanation on its own.