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.
And those. stratagems have won the highest credit by which a man most completely deceives the enemy and helps his friends.
While, then, the Athenians, still unprepared, are full of confidence and are thinking, so far as I can see, more of withdrawing than of staying where they are, while their tension of mind is relaxed and before they have got their thoughts together, I will take my own troops and if possible surprise them by a dash upon the centre of their army.
Then, Clearidas, the moment you see me pressing on and in all likelihood striking terror into them, do you suddenly throw open the gates and at the head of your own men and the Amphipolitans and the rest of our allies rush out upon them and make all haste to close with them at once. In this way there is the best hope to put them in a panic;
for a force that comes up afterwards has always more terror for an enemy than that with which he is already engaged.