History of the Peloponnesian War

The Lacedaemonians prepared, too, for their invasion of Attica, both in accordance with their own previous resolution, and at the instigation of the Syracusans and Corinthians, since they had heard of the reinforcements about to be sent from Athens to Sicily; that they might be stopped by an incursion being made into the country. Alcibiades also kept urgently advising them to fortify Decelea, and not to let the war rest.

But most of all had they gained confidence, because they thought that the Athenians, being engaged in a two-fold war with both themselves and the Siceliots, would be more easily subdued; and also because they considered them to have first broken the truce. For in the former course of hostilities they thought the guilt lay more on their own side, both because the Thebans had entered Plataea during a time of truce; and because, when it had been specified in the former treaty, that none should take up arms against others, if they were willing to submit to a judicial decision, they themselves had not listened to the Athenians when appealing to such a decision. On which account they considered that they were justly unsuccessful, and made both their misfortune at Pylus, and whatever other might have befallen them, a subject of [*]( Or, of religious scruple, as in some other passages.) serious reflection.