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.
But the greatest and most serious blow suffered by the Athenian army was the taking of Plemmyrium; for the work of bringing in provisions through the entrance to the harbour could no longer be carried on with safety (since the Syracusans lying in wait there with ships hindered this, and from now on the convoys could only make their entrance by fighting), and in general this event brought consternation and discouragement to the army.
After this the Syracusans sent out twelve ships under the command of Agatharchus, a Syracusan. One of these headed for the Peloponnesus, having on board some envoys who were to explain the situation in Sicily, that they were full of hope, and to urge the still more vigorous prosecution of the war on the continent of Greece. The other eleven ships sailed to Italy,[*](In Thucydides the term is used only of the part of the peninsula south of the river Laüs and Metapontum.) since they heard that boats laden with supplies for the Athenians were approaching. And falling in with these boats, they destroyed most of them;
and they also burned some timber in the territory of Caulonia, which was lying there ready for the Athenians to use in ship-building.
After this they went to Locri, and while they were lying there at anchor, one of the merchant-ships that had sailed from the Peloponnesus arrived in port, bringing some Thespian hoplites.
Taking these on board their ships, the Syracusans sailed along the coast toward home. But the Athenians, who were watching for them at Megara with twenty ships, captured one ship together with its crew, but they could not take the rest, which escaped to Syracuse. Skirmishing also occurred in the harbour about the piles which the Syracusans drove down in the sea in front of their old dockyards with the object that the ships might lie moored inside the piles and the Athenians might not sail up and ram their ships.