Cicero, On Behalf of Milo
4.10-11 (tr. N.H. Watts):
There does exist therefore, gentlemen, a law which is a law not of the statute-book, but of nature; a law which we possess not by instruction, tradition, or reading, but which we have caught, imbibed, and sucked in at Nature’s own breast; a law which comes to us not by education but by constitution, not by training but by intuition—the law, I mean, that, should our life have fallen into any snare, into the violence and the weapons of robbers or foes, every method of winning a way to safety would be morally justifiable. When arms speak, the laws are silent; they bid none to await their word, since he who chooses to await it must pay an undeserved penalty ere he can exact a deserved one.
Est igitur haec, iudices, non scripta, sed nata lex, quam non didicimus, accepimus, legimus, verum ex natura ipsa adripuimus, hausimus, expressimus, ad quam non docti, sed facti, non instituti, sed imbuti sumus, ut, si vita nostra in aliquas insidias, si in vim et in tela aut latronum aut inimicorum incidisset, omnis honesta ratio esset expediendae salutis; silent enim leges inter arma nec se exspectari iubent, cum ei, qui exspectare velit, ante iniusta poena luenda sit quam iusta repetenda.
[I]t is a truth instilled into civilized beings by reason, into barbarians by necessity, into mankind by custom, and even into brute beasts by Nature herself, that always and in all circumstances they should repel violence, by whatever means were in their power, from their persons, their heads, and their lives...
[H]oc et ratio doctis et necessitas barbaris et mos gentibus et feris etiam beluis natura ipsa praescripsit, ut omnem semper vim, quacumque ope possent, a corpore, a capite, a vita sua propulsarent...