History of the Peloponnesian War
Thucydides
Thucydides, Vol. 1-4. Smith, Charles Foster, translator. London and Cambridge, MA: Heinemann and Harvard University Press, 1919-1923.
He said that the Athenians were in the habit of passing the night in the city away from their arms, and if the Syracusans would come in full force at dawn on an appointed day against their army, they would close the gates on the Athenians in their city and set fire to the ships, and the Syracusans could attack the stockade and easily take the whole army; for there were many Catanaeans who would help them in this undertaking, and the men from whom he himself had come were ready now.
And the Syracusan generals, who were already confident as to the general situation, and intended even without this help to go against Catana, trusted the fellow much too incautiously, and at once, agreeing upon a day on which they would be there, sent him back; and themselves—the Selinuntians and some others of their allies being already present—made proclamation for the whole force of the Syracusans to take the field. And when their preparations were made and the days were near on which they had agreed to come, they proceeded towards Catana and bivouacked at the River Simaethus in the territory of Leontini.
But the Athenians, when they learned of their approach, took all their own army and such of the Sicels or others as had joined them, and embarking on their ships and boats sailed under cover of night against Syracuse.
And they disembarked at daybreak at a point opposite the Olympieium, where they proposed to occupy a camping-place; but the Syracusan horsemen, who were the first to reach Catana and found there that the whole army was gone, turned about and announced this to the infantry, and all then turned back at once and hastened to bring aid to the city.
Meanwhile the Athenians, undisturbed, as the Syracusans had a long way to go, settled their army in a suitable position, where they could begin a battle whenever they wished and the Syracusan horsemen would annoy them the least either in the actual fighting or before; for on one side walls and houses and trees and a swamp furnished a barrier, on the other side a line of cliffs.