Laudator Temporis Acti

Polybius 6.10.3-5 (tr. Ian Scott-Kilvert):

[3] For just as rust eats away iron, and woodworms or ship-worms eat away timber, and these substances even if they escape any external damage are destroyed by the processes which are generated within themselves, [4] so each constitution possesses its own inherent and inseparable vice. Thus in kingship the inbred vice is despotism, in aristocracy it is oligarchy, [5] and in democracy the brutal rule of violence, and it is impossible to prevent each of these kinds of government, as I mentioned above, from degenerating into the debased form of itself.

[3] καθάπερ γὰρ σιδήρῳ μὲν ἰός, ξύλοις δὲ θρῖπες καὶ τερηδόνες συμφυεῖς εἰσι λῦμαι, δι᾽ ὧν, κἂν πάσας τὰς ἔξωθεν διαφύγωσι βλάβας, ὑπ᾽ αὐτῶν φθείρονται τῶν συγγενομένων, [4] τὸν αὐτὸν τρόπον καὶ τῶν πολιτειῶν συγγεννᾶται κατὰ φύσιν ἑκάστῃ καὶ παρέπεταί τις κακία, βασιλείᾳ μὲν ὁ μοναρχικὸς λεγόμενος τρόπος, ἀριστοκρατίᾳ δ᾽ ὁ τῆς ὀλιγαρχίας, [5] δημοκρατίᾳ δ᾽ ὁ θηριώδης καὶ χειροκρατικός, εἰς οὓς οὐχ οἷόν τε μὴ οὐ πάντα τὰ προειρημένα σὺν χρόνῳ ποιεῖσθαι τὰς μεταστάσεις κατὰ τὸν ἄρτι λόγον.