History of the Peloponnesian War

For the Syracusans and their allies, on gaining the advantage, were cheering each other with no little shouting, (it being impossible during the night to express themselves in any other way,) and at the same time were receiving the charge of their assailants: and the Athenians were in search of one another, and thought that whoever met them was a foe, even though he might be a friend, belonging to those who were now flying back. And by their frequently asking for the watchword, because they could not by any other means distinguish them, they both caused great confusion on their own side by all asking at once, and made it known to the enemy;

while theirs, on the other hand, they did not so easily discover, because, as they were victorious and not dispersed, they were better recognised by each other. So that if they fell in with any of the enemy with the advantage of numbers en their own side, the Syracusans escaped from them, inasmuch as they knew the Athenian watchword;

but if they themselves [in such a case] did not answer, they were put to the sword. But what especially and in the greatest degree hurt them, was the singing of their hymns; for as it was very similar on each side, it occasioned perplexity. For the Argives, the Corcyraeans, and all of the Dorian race that were with the Athenians, struck terror into them whenever they raised their paean;

and so did the enemy likewise. Thus having at last, when once they were thrown into disorder, come into collision with each other in different parts of the army, friends with friends, and countrymen with countrymen, they were not only full of fear, but even closed in battle with each other, and were with difficulty parted.