History of the Peloponnesian War

For in this case they were making their expedition openly, as they imputed to the Athenians a want of power to oppose them, because no numerous fleet belonging to them was yet visible. And so, according to their resolution, they immediately took across one and twenty ships.

But when they were urgent for setting sail, the Corinthians were not disposed to accompany them before they had kept the Isthmian festival, for which that was the time. Agis expressed to them his willingness that they (according to what they urged) should not break the Isthmian truce, but that he should make the expedition on his own responsibility.

When, however, the Corinthians did not agree to this, but a delay was caused in the matter, the Athenians the more easily gained intelligence of the designs of the Chians; and sending Aristocrates, one of their generals, charged them with the fact, and on their denying it, commanded them to send with them some ships, as a pledge of good faith in their alliance.