My focus of attention is the great plague of Athens. However, before analysing the impact of the plague upon contemporary Athenian society, I should like, if I may so describe it, to examine Athenian impact upon the plague. More specifically, I wish to examine Thucydides's treatment of the plague. Thucydides provides our only contemporary account.
The Peloponnesian War broke out in 431 bc. In the early summer of the second year of the war the Peloponnesians again invaded Attica and laid waste to the countryside, whose inhabitants had taken refuge within the Long Walls. The city consequently became seriously overcrowded. Thucydides himself mentions this overcrowding (The Peloponnesian War, Book II, Chapter 52) and Aristophanes, with comic hyperbole, speaks in the Knights (792ff) of the refugees squatting in casks and birds' nests. A few days after the incursion of the Lacedaimonian army into Attica plague broke out in Athens – a pestilence, we are told, of unprecedented mortality. The plague raged ferociously during that year and the next. It subsided and then broke out again in 427 bc, wiping out, it appears, one third of the population of the city (a higher proportion, incidentally, than that of medieval London carried off by the Black Death).
The spread of the plague to Athens and its impact upon that overcrowded city is described by Thucydides in the second book of his History of the Peloponnesian War (Chapters 47–54):
 In the first days of summer in the second year of the war the Lacedaimonians and their allies, with two-thirds of their forces as before, invaded Attica. […]