History of the Peloponnesian War

Thucydides

Thucydides, Vol. 1-4. Smith, Charles Foster, translator. London and Cambridge, MA: Heinemann and Harvard University Press, 1919-1923.

But the Athenians went out against the Lacedaemonians with their whole force and with one thousand Argives and contingents of the several allies, the whole body amounting to fourteen thousand men.

And they undertook the expedition against them because they believed that they were at a loss how to get through, and partly too on a suspicion of a plot to overthrow the democracy.