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.
as they sailed along the shore of Libya they had joined forces with the Euesperitae, who were being besieged by the Libyans, and had defeated the latter; and sailing thence along the coast to Neapolis, an emporium of the Carthaginians, from which place the distance to Sicily is shortest—two days and one night—and from there crossing to Sicily, they arrived at Selinus.
As soon as these reinforcements arrived, the Syracusans began their preparations to attack the Athenians again on both elements—by sea and by land. The Athenian generals, on the other hand, seeing that the enemy had been reinforced by a fresh army, while their own situation was not only not improving, but on the contrary was daily growing worse in all respects, and especially through the distress caused by the sickness among the troops, repented that they had not moved away before. And since even Nicias no longer opposed as earnestly as before, but only urged that the matter be not openly put to a vote, they sent out word as secretly as possible to all the officers for a departure by sea from the camp, and that they should be ready whenever the signal should be given.
But after all was ready and when they were about to make their departure, the moon, which happened then to be at the full, was eclipsed.[*](August 27, 413 B.C.) And most of the Athenians, taking the incident to heart, urged the generals to wait. Nicias also, who was somewhat too much given to divination and the like, refused even to discuss further the question of their removal until they should have waited thrice nine days, as the soothsayers prescribed. Such, then, was the reason why the Athenians delayed and stayed on.
The Syracusans on their part, on learning about this, were far more aroused than before and determined not to give the Athenians any respite, seeing that these had now of their own act confessed themselves no longer superior either with their fleet or with their land-force, for otherwise they would not have laid plans for their departure; and at the same time, because they did not want them to settle down somewhere else in Sicily where it would be more difficult to carry on war against them, they were determined to force them to fight a sea-battle as quickly as possible on the spot, in a place that suited themselves.