M. Tullius Cicero, De Officiis
Walter Miller, Ed.

[37] There is extant, too, a letter of the elder Marcus Cato to his son Marcus, in which he writes that he has heard that the youth has been discharged by the consul,¹ when he was serving in Macedonia in the war with Perseus. He warns him, therefore, to be careful not to go into battle; for, he says, the man who is not legally a soldier has no right to be fighting the foe.

12. This also I observe—that he who would properly have been called “a fighting enemy” (perduellis) was called “a guest” (hostis), thus relieving the ugliness of the fact by a softened expression; for “enemy” (hostis) meant to our ancestors [p. 41] what we now call “stranger” (peregrinus). This is proved by the usage in the Twelve Tables: “Or a day fixed for trial with a stranger” (hostis). And again: “Right of ownership is inalienable for ever in dealings with a stranger” (hostis). What can exceed such charity, when he with whom one is at war is called by so gentle a name? And yet long lapse of time has given that word a harsher meaning: for it has lost its signification of “stranger” and has taken on the technical connotation of “an enemy under arms.”