Xenophon (c. 420-350 BCE)
“We have much more horror of a traitor than of an enemy, since it is harder to guard against hidden dangers than open ones. And we hate traitors more than enemies, since with our enemies we can make peace and become friends again, but when we find that we have been betrayed by someone, we can never under any circumstances make peace with him and can never trust him.”
- A History of My Times (Hellenica, II.3.29) by Xenophon, translated by Rex Warner. New York: Penguin Classics, 1966, 1979.