History of the Peloponnesian War

For though the moon shined bright, yet they saw one another no otherwise than as by the moonlight was likely, so as to see a body, but not be sure whether it were a friend or not.

And the men of arms on both sides, being not a few in number, had but little ground to turn in. Of the Athenians, some were already overcome, others went on in their first way. Also a great part of the rest of the army was already part gotten up and part ascending, and knew not which way to march. For after the Athenians once turned their backs, all before them was in confusion;

and it was hard to distinguish of anything for the noise. For the Syracusians and their confederates prevailing encouraged each other and received the assailants with exceeding great shouts (for they had no other means in the night to express themselves); and the Athenians sought each other and took for enemies all before them, though friends and of the number of those that fled, and by often asking the word, there being no other means of distinction, all asking at once they both made a great deal of stir amongst themselves and revealed the word to the enemy. But they did not in like manner know the word of the Syracusians, because these, being victorious and undistracted, knew one another better;

so that when they lighted on any number of the enemy, though they themselves were more, yet the enemy escaped as knowing the watchword; but they, when they could not answer, were slain.