History of the Peloponnesian War
Thucydides
Thucydides. The history of the Peloponnesian War, Volume 1-2. Dale, Henry, translator. London: Heinemann and Henry G. Bohn, 1851-1852.
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.
And now, as they were being pursued, the greater part threw themselves down the cliffs, and perished; as the way down again from Epipolae was narrow. And when those who escaped from the heights had reached the plain, though many of them, especially such as belonged to the former armament, through their greater acquaintance with the localities escaped safely to the camp, some of those who had lately arrived lost their way, and wandered about the country; and these, when it was day, the Syracusan horse intercepted, and put to the sword.
The next day the Syracusans erected two trophies, one on Epipolae, where the enemy's approaches had been made, and the other on the spot where the Boeotians first withstood them; while the Athenians recovered their dead under truce.
No few were killed, both of themselves and their allies, though still more arms were taken than in proportion to the number of the dead: for of those who were compelled to leap down the cliffs unencumbered by their shields, though some perished, yet others escaped with their lives.
After this, the Syracusans being again, as before, restored to confidence on the strength of such unexpected good fortune, despatched Sicanus with fifteen ships to Acragas, which was torn by factions, to induce the city to join them, if he could: while Gylippus again went by land to the other parts of Sicily to bring more forces, being in hope of even taking the Athenian lines by storm, since the affair on Epipolae had turned out as it did.