We must ever stand . . . and make watch, for our adversary is never idle: but when he is most calm and still, when he feigneth to flee or to make truce, even then most of all he imagineth guile: and thou hast never more heed to keep watch than when he maketh countenance or semblance of peace. Thou hast never less need to fear than when he assaulteth thee with open war. Therefore let thy first care be that thy mind be not unarmed. We arm our body, because we would have no need to fear the dagger . . . Shall we not arm our mind likewise, that he might be in safeguard?

Excerpted from Chapter II, Enchiridion Militis Christiani (1501), by Desiderius Erasmus.

(A much simplified list of the Erasmus’ twenty-two principles comprises appendix A of Grossman’s On Combat, whence I discovered this, and about which I will probably have more to say later.)