In the very beginning of summer the Peloponnesians and their allies, with two-thirds of their forces as before, invaded Attica under the command of Archidamus, King of Lacedaemon. After they had settled in, they started wasting the country around them.

They had not been in Attica for many days when the plague first began among the Athenians. Although it was said to have broken out in many other places, particularly in Lemnos, no one could remember a disease that was so great or so destructive of human life breaking out anywhere before. Doctors, not knowing what to do, were unable to cope with it at first, and no other human knowledge was any use either. The doctors themselves died fastest, as they came to the sick most often. Prayers in temples, questions to oracles—all practices of that kind turned out to be useless also, and in the end people gave them up, defeated by the evil of the disease.

They say it first began in the part of Ethiopia that is above Egypt, and from there moved down to Egypt and Libya and into most of the Persian Empire. It hit Athens suddenly, first infecting people in Piraeus [the port of Athens], with the result that they said the Peloponnesians must have poisoned the water tanks (they had no wells there at the time). Afterwards the plague moved inland to the city, where people died of it a good deal faster. Now anyone, doctor or layman, may say as much as he knows about where this probably came from, or what causes he thinks are powerful enough to bring about so great a change. For my part, I will only say what it was like: I will show what to look for, so that if the plague breaks out again, people may know in advance and not be ignorant. I will do this because I had the plague myself, and I myself saw others who suffered from it.