History of the Peloponnesian War

Meanwhile they would take only half the ships across the Isthmus first, and let those sail off at once, in order that the Athenians might attend less to the departing squadron than to those to be taken across afterwards,

as no care had been taken to keep this voyage secret through contempt of the impotence of the Athenians, who had as yet no fleet of any account upon the sea. Agreeably to this determination twenty-one vessels were at once conveyed across the Isthmus.

They were now impatient to set sail, but the Corinthians were not willing to accompany them until they had celebrated the Isthmian festival, which fell at that time. Upon this Agis proposed to them to save their scruples about breaking the Isthmian truce by taking the expedition upon himself.