Plato, Laws 678c

καὶ μάλα πρέπει τοῦθʼ οὕτως. ἐκ γὰρ τῶν ὑψηλῶν εἰς τὰ πεδία καταβαίνειν, οἶμαι, πᾶσιν φόβος ἔναυλος ἐγεγόνει. πῶς δʼ οὔ; ἆρʼ οὐχ ἅσμενοι μὲν ἑαυτοὺς ἑώρων διʼ ὀλιγότητα ἐν τοῖς περὶ ἐκεῖνον τὸν χρόνον, πορεῖα δέ, ὥστʼ ἐπʼ ἀλλήλους τότε πορεύεσθαι κατὰ γῆν ἢ κατὰ θάλατταν, σὺν ταῖς τέχναις ὡς ἔπος εἰπεῖν πάντα σχεδὸν ἀπωλώλει; συμμίσγειν οὖν ἀλλήλοις οὐκ ἦν οἶμαι σφόδρα δυνατόν· σίδηρος γὰρ

Yes, that is most likely. For they all, I fancy, felt as it were still ringing in their ears a dread of going down from the highlands to the plains. Of course. And because there were so few of them round about in those days, were they not delighted to see one another, but for the fact that means of transport, whereby they might visit one another by sea or land, had practically all perished along with the arts? Hence intercourse, I imagine, was not very easy.