Passage 8.27.1
ἡ δὲ Μεγάλη πόλις νεωτάτη πόλεών ἐστιν οὐ τῶν Ἀρκαδικῶν μόνον ἀλλὰ καὶ τῶν ἐν Ἕλλησι, πλὴν ὅσων κατὰ συμφορὰν ἀρχῆς τῆς Ῥωμαίων μεταβεβήκασιν οἰκήτορες· συνῆλθον δὲ ὑπὲρ ἰσχύος ἐς αὐτὴν οἱ Ἀρκάδες, ἅτε καὶ Ἀργείους ἐπιστάμενοι τὰ μὲν ἔτι παλαιότερα μόνον οὐ κατὰ μίαν ἡμέραν ἑκάστην κινδυνεύοντας ὑπὸ Λακεδαιμονίων παραστῆναι τῷ πολέμῳ, ἐπειδὴ δὲ ἀνθρώπων πλήθει τὸ Ἄργος ἐπηύξησαν καταλύσαντες Τίρυνθα καὶ Ὑσιάς τε καὶ Ὀρνεὰς καὶ Μυκήνας καὶ Μίδειαν καὶ εἰ δή τι ἄλλο πόλισμα οὐκ ἀξιόλογον ἐν τῇ Ἀργολίδι ἦν, τά τε ἀπὸ Λακεδαιμονίων ἀδεέστερα τοῖς Ἀργείοις ὑπάρξαντα καὶ ἅμα ἐς τοὺς περιοίκους ἰσχὺν γενομένην αὐτοῖς.
Now Megalopolis is the youngest city, not only among Arcadian cities but also among all the Greek ones, except for those whose inhabitants have changed under disaster in the time of Roman rule. The Arcadians came together into it for the sake of strength, being aware that the Argives, in still earlier days, had been in nearly daily peril of war at the hands of Sparta, but after they enlarged Argos by abandoning Tiryns, Hysiae, Orneae, Mycenae, Mideia, and any other insignificant town in Argolis that existed at the time, the Argives thereafter became freer from fear of the Spartans and also gained power over their neighbors.