History of the Peloponnesian War

Indeed the first and chiefest cause of the ruin of the Athenian army was the capture of Plemmyrium; even the entrance of the harbor being now no longer safe for carrying in provisions, as the Syracusan vessels were stationed there to prevent it, and nothing could be brought in without fighting; besides the general impression of dismay and discouragement produced upon the army.

After this the Syracusans sent out twelve ships under the command of Agatharchus, a Syracusan. One of these went to Peloponnese with ambassadors to describe the hopeful state of their affairs, and to incite the Peloponnesians to prosecute the war there even more actively than they were now doing, while the eleven others sailed to Italy, hearing that vessels laden with stores were on their way to the Athenians.