" the only way to render a battalion invincible. For men will desert those of the same tribe or family, nay, their very children and parents; but never any enemy could pierce or penetrate between a lover and his darling minion, in whose sight many times when there is no necessity the lover delights to show his courage and contempt of danger; like Thero the Thessalian, who clapping his left hand to the wall, and then drawing his sword, struck off his thumb, thereby challenging his rival to do the same. Or like another, who falling in battle upon his face, as his enemy was about to follow his blow, desired him to stay till he could turn, lest his male concubine should see that he had been wounded in the back.
And therefore we find that the most warlike of nations are most addicted to love, as the Boeotians, Lacedaemonians, and Cretans. And among the most ancient heroes none were more amorous than Meleager, Achilles, Aristomenes, Cimon, and Epaminondas; the latter of which had for his male concubines Asopichus and Caphisodorus, who was slain with him at the battle of Mantinea and lies buried very near him." Plutarch, Amatorius (you can find the whole text at the Perseus Project)