Plato, Laws 637c

βλακικώτερα· ταχὺ γάρ σου λάβοιτʼ ἄν τις τῶν παρʼ ἡμῶν ἀμυνόμενος, δεικνὺς τὴν τῶν γυναικῶν παρʼ ὑμῖν ἄνεσιν. ἅπασιν δὴ τοῖς τοιούτοις, καὶ ἐν Τάραντι καὶ παρʼ ἡμῖν καὶ παρʼ ὑμῖν δέ, μία ἀπόκρισις ἀπολύεσθαι δοκεῖ τοῦ μὴ κακῶς ἔχειν ἀλλʼ ὀρθῶς· πᾶς γὰρ ἀποκρινόμενος ἐρεῖ θαυμάζοντι ξένῳ, τὴν παρʼ αὐτοῖς ἀήθειαν ὁρῶντι, μὴ θαύμαζε, ὦ ξένε· νόμος ἔσθʼ ἡμῖν οὗτος, ἴσως δʼ ὑμῖν περὶ αὐτῶν τούτων

but where this is relaxed they are quite stupid. An Athenian in self-defence might at once retaliate by pointing to the looseness of the women in your country. Regarding all such practices, whether in Tarentum, Athens or Sparta, there is one answer that is held to vindicate their propriety. The universal answer to the stranger who is surprised at seeing in a State some unwonted practice is this: Be not surprised, O Stranger: such is the custom with us: with you, perhaps, the custom in these matters is different.