History of the Peloponnesian War

And things which before were spoken of from hearsay, but scantily confirmed by fact, were rendered not incredible; both about earthquakes, which at once extended over the greatest part of the world, and most violent at the same time; and eclipses of the sun, which happened more frequently than was on record of former times; and great droughts in some parts, and from them famines also; and what hurt them most, and destroyed a considerable part—the plague. For all these things fell upon them at once along with this war:

which the Athenians and Peloponnesians began by breaking the thirty years' truce after the taking of Euboea.

As for the reason why they broke it, I have first narrated their grounds of complaint and their differences, that no one might ever have to inquire from what origin so great a war broke out amongst the Greeks. For the truest reason, though least brought forward in words, I consider to have been, that the Athenians, by becoming great, and causing alarm to the Lacedaemonians, compelled them to proceed to hostilities.