Plutarch, Themistocles
Bernadotte Perrin, Ed.

Some tell the story that while Themistocles was thus speaking from off the deck of his ship, an owl was seen to fly through the fleet from the right and alight in his rigging; wherefore his hearers espoused his opinion most eagerly and prepared to do battle with their ships. [2] But soon the enemy's armament beset the coast of Attica down to the haven of Phalerum, so as to hide from view the neighboring shores; then the King in person with his infantry came down to the sea, so that he could be seen with all his hosts; and presently, in view of this junction of hostile forces, the words of Themistocles ebbed out of the minds of the Hellenes, and the Peloponnesians again turned their eyes wistfully towards the Isthmus and were vexed if any one spake of any other course; nay, they actually decided to withdraw from their position in the night, and orders for the voyage were issued to the pilots. [3] Such was the crisis when Themistocles, distressed to think that the Hellenes should abandon the advantages to be had from the narrowness of the straits where they lay united, and break up into detachments by cities, planned and concocted the famous affair of Sicinnus.

This Sicinnus was of Persian stock, a prisoner of war, but devoted to Themistocles, and the paedagogue of his children. [4] This man was sent to Xerxes secretly with orders to say: ‘Themistocles the Athenian general elects the King's cause, and is the first one to announce to him that the Hellenes are trying to slip away, and urgently bids him not to suffer them to escape, but, while they are in confusion and separated from their infantry, to set upon them and destroy their naval power.’ [5] Xerxes received this as the message of one who wished him well, and was delighted, and at once issued positive orders to the captains of his ships to man the main body of the fleet at their leisure, but with two hundred ships to put to sea at once, and encompass the strait round about on every side, including the islands in their line of blockade, that not one of the enemy might escape. [6]

While this was going on, Aristides the son of Lysimachus, who was the first to perceive it, came to the tent of Themistocles, who was no friend of his, nay through whom he had even been ostracized, as I have said; and when Themistocles came forth from the tent, Aristides told him how the enemy surrounded them. Themistocles, knowing the tried nobility of the man, and filled with admiration for his coming at that time, told him all about the Sicinnus matter, and besought him to join in this desperate attempt to keep the Hellenes where they were,—admitting that he had the greater credit with them,—in order that they might make their sea-fight in the narrows. [7] Aristides, accordingly, after bestowing praise upon Themistocles for his stratagem, went round to the other generals and trierarchs inciting them on to battle. And while they were still incredulous in spite of all, a Tenian trireme appeared, a deserter from the enemy, in command of Panaetius, and told how the enemy surrounded them, so that with a courage born of necessity the Hellenes set out to confront the danger.