Marcus Tullius Cicero, Cyrus R. Edmonds (1863). “Three Books of Offices; Or, Moral Duties: Also His Cato Major, an Essay on Old Age; Laelius, an Essay on Friendship; Paradoxes; Scipio's Dream; and Letter to Quintus on the Duties of a Magistrate. Literally Translated, with Notes, Designed to Exhibit a Comparative View of the Opinions of Cicero, and Those of Modern Moralists and Ethical Philosophers”, p.21
"Letters to Atticus" (1st century B.C.), as quoted in "Words on war: military quotations from ancient times to the present", book by Jay M. Shafritz, 1990.