Idea found in Plautus, Stich, IV. 1. 16. Ovid, Epigram ex Ponto, II. 3. 23. Ovid, Trist. I. 9. 5. Ennius, Cic. Amicit, Chapter XVII. Metastasio, Olimpiade, III. 3. Johann Gottfried Herder, Denksprüche. Pedro Calderón de la Barca, Secret in Words, Act III, scene 3. Menander, Ex Incest. Comoed, p. 272. Aristotle, Ethics VIII. 4. Euripides, Hecuba, line 1226.https://en.wikiquote.org/wiki/Friendship