History of the Peloponnesian War

Having, therefore, crossed over with a body of troops and his ships, he completed the building of three forts; in which were deposited the greater part of the stores; the larger boats and the fast-sailing ships being now also moored there. And in consequence of this, it was chiefly at that title that the wasting of the crews first began.

For as they had but a scanty supply of water, and that not close at hand; and, moreover, as the sailors from time to time went out to gather firewood, they were cut off by the Syracusan horse, which had the command of the country. For a third part of their cavalry had been posted by the Syracusans in the small town in the Olympieum, with an eye to the troops on Plemyrium, to prevent their marching out to commit ravages.

Meanwhile Nicias learned that the rest of the Corinthian ships also were sailing to the island, and sent twenty vessels to watch for them, with orders to be on the look-out for them about Locri, Rhegium, and the approaches to Sicily.