The Persian War was the greatest action of earlier times, yet that was 23 speedily settled in two battles at sea and two on land. But the present war lasted a long time and in the course of it Greece was afflicted with sufferings unprecedented in any comparable period of time. Never before were so many cities captured and laid waste – some by barbarians and others by Greeks fighting wars among themselves (and some of these cities went on to be resettled with new inhabitants after they had been captured).Never before were so many men made exiles, never before was there so much slaughter – some in the course of the war itself and some as a result of internal conflicts. And things that in the past were reported on the basis of hearsay, where the actual evidence was rather flimsy, now ceased to be incredible: earthquakes, which spread to most parts of the world and were also very violent; eclipses of the sun, which became more frequent than those in past memory; great droughts in some places, and arising from them both famines and the most damaging thing of all, which wiped out part of the population – the deadly plague. All these disasters descended on them at the same time along with this war.

The Athenians and Spartans began the war when they broke the thirty-year truce they made after the capture of Euboea. To explain why they broke it I first set out the reasons they gave and the matters of dispute between them so that no one in future ever need enquire how it came about that so great a war arose among the Greeks. I consider the truest cause, though the one least openly stated, to be this: the Athenians were becoming powerful and inspired fear in the Spartans and so forced them into war.