History of the Peloponnesian War
Thucydides. The Peloponnesian War. London, J. M. Dent; New York, E. P. Dutton. 1910.
Aware of this, the Athenian generals determined to draw them out in mass as far as possible from the city, and themselves in the meantime to sail by night along shore, and take up at their leisure a convenient position. This they knew they could not so well do, if they had to disembark from their ships in front of a force prepared for them, or to go by land openly. The numerous cavalry of the Syracusans (a force which they were themselves without), would then be able to do the greatest mischief to their light troops and the crowd that followed them; but this plan would enable them to take up a position in which the horse could do them no hurt worth speaking of, some Syracusan exiles with the army having told them of the spot near the Olympieum, which they afterwards occupied. In pursuance of their idea, the generals imagined the following stratagem.
They sent to Syracuse a man devoted to them, and by the Syracusan generals thought to be no less in their interest; he was a native of Catana, and said he came from persons in that place, whose names the Syracusan generals were acquainted with, and whom they knew to be among the members of their party still left in the city.
He told them that the Athenians passed the night in the town, at some distance from their arms, and that if the Syracusans would name a day and come with all their people at daybreak to attack the armament, they, their friends, would close the gates upon the troops in the city, and set fire to the vessels, while the Syracusans would easily take the camp by an attack upon the stockade. In this they would be aided by many of the Catanians, who were already prepared to act, and from whom he himself came.