The Peloponnesian War was fought between 431-404 BC, with an agreed peace between the years 421 and 413 BC. During the first part of the war, known as the Archidamian War, the City of Athens survived a devastating plague that appeared in the years 430, 429 and 427 BC. The death toll is not certain, but our main source, Thucydides (3.87), suggests that upto one third of the fighting stength of the city died as a result. This had a strong impact on the people of Athens, not least because their most prominent politician and strategist, Pericles, died after contracting the disease.

However, the plague did not stop the Athenians from succesfully engaging in the ongoing war. During this period of infection, they still managed a sustained two year siege of Potidaea, continued their strategic policy of raiding the coast of the Peloponnese, and maintained control of their empire. In 425 BC they managed a famous victory over the Spartans at Pylos, in enemy territory. As a result of this victory, the Athenians captured some Spartan citizens and took them to Athens as prisoners of war. The Spartans panicked and, with the desire for war subsiding in the Spartan populace, they asked the Athenians for a peace treaty. The Athenians refused.

In 424 BC, the Athenians put a large force including 7,000 citizen-hoplites into the field at Delium where they were defeated and lost 1,000 of their men. Even then, the Athenians continued the war, and it wasn’t until the important city of Amphipolis was finally lost in 422 BC that the Athenians agreed to peace in 422/1 BC. The Decelean War that Athens would actually lose started eight year later, in 413 BC. following the Athenians’ failed military expedition to Syracuse in Sicily. It was the loss of manpower, money, and ships as a result of their defeat in Sicily, alligned with the now growing revolts throught their empire, which impacted the Athenians so gravely. But even then, they would not be defeated for another nine years.

So, when you consider that the plague did not entice the Athenians to look for peace, that they actually held the upperhand for much of the war, and defeat did not occur until almost 23 years after the final plague outbreak – then it must be concluded that while this plague was devastating for the Athenian people, it was not responsible for the Athenian defeat.