Thucydides and the Plague of Athens

The “Plague of Athens” was a severe epidemic, which struck the city between 430 and 427 B.C.E.; reemerging there in 425 B.C.E. It is believed to have originated in Ethiopia, and then to have spread throughout the Mediterranean. It hit Athens early during the Peloponnesian War (431-404 B.C.E), at a time when the city was under siege by Sparta. The Plague claimed the lives of about a third of Athens’ citizens. Yet the extent, to which it might have contributed to the ultimate Spartan victory in the war, or to the eventual decline of the Athenian empire, is not known.

The Athenian historian, Thucydides, in his History of the Peloponnesian War, provides the only known eye-witness account of the Plague. For that reason alone, Thucydides’ account is of great historical interest. Yet Thucydides also set down his own truly remarkable (considering the time) insights into the epidemiology of the Plague.

Thucydides (460-395 B.C.E.)
Thucydides (460-395 B.C.E.)

First, Thucydides noted that the most densely populated sections of Athens had the highest frequency of Plague victims. [The Athenian leader, Pericles, responded to the Spartan siege by moving people into Athens from the countryside. The resulting overcrowding unwittingly worsened the epidemic.] Second, Thucydides noted that physicians had highest likelihood of any group in the population of succumbing to the Plague. [Physicians were the ones most frequently exposed to affected individuals.] Moreover, Thucydides reported that the Plague could be transported from one place to another; an observation he made during the Athenian siege of Poteida (430/429 B.C.E.), when a reinforcing body of Athenian soldiers transmitted the Plague to Athenian soldiers already at Poteida. From this observation, Thucydides deduced that the Plague was not due to some “malign influence” confined to Athens and its immediate environs, as would have been consistent with Greek medical theory of the day (see below). [Incidentally, Plato tells us in his dialogues that Socrates was a veteran of the siege at Poteida.]

Taken together, these observations led Thucydides to put forward, perhaps for the first time, the notion that an affected individual might pass on a disease, directly, to another individual who is not yet affected. In contrast, medical theory of the day held that epidemics result from miasma: poisonous vapors, which inflicted anyone who might breathe them. Miasma could be caused by the weather, by the stars, or by the displeasure of the gods.

Miasma readily explained why large numbers of people could become ill at the same time. They simply breathed the same air. Yet Thucydides was in fact proposing something radically different; that is, contagions. And he did so twenty-three centuries before Pasteur, Lister, Koch and others in the 19th century established our modern germ theory of disease! Before then, western medicine continued to attribute epidemics to miasma.

Another of Thucydides’ key observations was that individuals who recovered from the Plague were resistant to future attacks. Moreover, he recognized that their resistance was specific. That is, survivors of the Plague were resistant to further attacks of the Plague, but not to other diseases. This insight too was remarkable since our modern concept of specific acquired immunity came even later than our concept of infectious disease. Thucydides’ deduction may have influenced his fellow Athenians, since those individuals who survived the plague comprised the few who were willing to care for those who fell ill.

Thucydides could not know the nature of the contagion he was proposing, although he thought it might be a fluid. And, while the epidemic in Athens is referred to today as a plague, it almost certainly was not bubonic or pneumonic plague.

Some modern references to the Plague of Athens presume that it was smallpox. Thucydides does mention the body “breaking out into small postules and ulcers,” and other aspects of his description of the disease are consistent with smallpox. Yet Thucydides also tells us that dogs too were susceptible to the Plague. However, humans are the only host for smallpox.

At any rate, the exact cause of the Plague of Athens is not known for certain. Modern experts have attributed it to a variety of pathogens, including Yesinia pestis, typhus, anthrax, measles, and even Ebola, in addition to smallpox. Yet none of the diseases associated with any contemporary pathogen exactly matches Thucydides’ description of the Plague of Athens. It is possible that the pathogen responsible for the Plague, and the Plague’s symptoms as well, might have changed over 24 centuries. Another possibility is that the pathogen responsible for the Plague has since become extinct.

Thucydides’ insights are not nearly as well known today as they ought to be. Perhaps that is because they had no lasting influence on his contemporaries or, for that matter, on those who came later. Consider how the history of medical science might have been different if Hippocrates, and others of Thucydides’ contemporaries, had been influenced by his observations.

How might we explain why Thucydides’ insights were largely ignored by his contemporaries and, indeed, lost to western medicine? One reason is that the ancient Greeks had precious little scientific knowledge that might have enabled them to understand the Plague. Moreover, Thucydides’ Athenian contemporaries made little distinction between medicine and religion. For instance, Sophocles (one of the great dramatists of classical Greece) believed that the plague had a supernatural cause, and that an oracle, rather than a physician, needed to be consulted for its resolution.

Hippocrates (about 460 to 370 B.C.E.) may have been the first physician to believe that diseases have natural causes, rather than being punishments inflicted by the gods. However, none of Hippocrates’ writings suggest the concept of a contagion. In any case, after Hippocrates’ death, the practice of Greek medicine actually regressed back to a more superstitious state.

What’s more, contrary to popular opinion; the Greeks did not actually invent the scientific method. Nor were their theories developed with the intent of experimental verification. Aristotle’s science held that nature did what pure logic suggested it should do. For example, he said that heavier objects fall faster than lighter objects, because it is their purpose to do so. Neither Aristotle nor his contemporaries actually looked to see if heavier objects indeed fall faster than lighter ones (they don’t). In fact, the first individual known to have actually tested this premise was Galileo (1564-1642). Only afterwards did observation become the basis for western science. And, this transition was not easy since, as we know well, the powerful churchmen of Galileo’s day rejected the concept that the universe might be governed by natural laws, since that notion might be at odds with the omnipotence of God.


Hays, J. N., Epidemics and Pandemics: Their Impacts on Human History, ABC-CLIO, Inc., Santa Barbara, California, 2005.

Holladay, A.J., and J.C.F. Poole. 1979. The Plague of Athens, The Classical Quarterly 29:282-300.

Related Postings:

Edward Jenner and the Smallpox Vaccine, posted on the blog September 16, 2014.

Smallpox in the New World: Vignettes featuring Hernan Cortes, Francisco Pizarro, and Lord Jeffry Amherst, posted on the blog February 24, 2014.





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