History of the Peloponnesian War

As for the Lacedaemonians, they happened to be celebrating a festival when they got word of the undertaking, and made light of it, thinking that the Athenians would not await their attack when they got ready to take the field, or, if they should, that they could easily take the place by force;

and the fact also that their army was still in Attica had something to do with their delay. The Athenians in six days completed the wall on the side toward the land and at such other points as most needed it, and left Demosthenes there with five ships to defend it; they then took the main body of the fleet and hastened on their voyage to Corcyra and Sicily.