Passage 7.12.9
καί σφισιν ἀπεκρίνατο ἡ βουλὴ ἀποστέλλειν πρέσβεις, οἳ κρινοῦσιν ὅσα Λακεδαιμονίοις καὶ Ἀχαιοῖς διάφορα ἦν ἐς ἀλλήλους. καὶ τοῖς ἐκ Ῥώμης πρέσβεσι σχολαιτέρα πως ἐγίνετο ἡ ὁδός, ὥστε ἐξαπατᾶν ὑπῆρχεν ἐξ ἀρχῆς Διαίῳ τε Ἀχαιοὺς καὶ Μεναλκίδᾳ Λακεδαιμονίους· τοὺς μὲν δὴ παρῆγεν ὁ Δίαιος ὡς τὰ πάντα ἕπεσθαι Λακεδαιμόνιοί σφισιν ὑπὸ τῆς Ῥωμαίων βουλῆς εἰσιν ἐγνωσμένοι, Λακεδαιμονίους δὲ ὁ Μεναλκίδας ἠπάτα παντελῶς τοῦ συνεδρεύειν ἐς τὸ Ἀχαϊκὸν ὑπὸ Ῥωμαίων αὐτοὺς ἀπηλλάχθαι.
And the Senate answered them that it would send envoys to arbitrate all the matters of dispute between the Lacedaemonians and the Achaeans. But the journey of the ambassadors from Rome was somewhat delayed, so that Diaeus from the very beginning deceived the Achaeans, and Menalcidas the Lacedaemonians. Diaeus led the Achaeans to believe that the Roman Senate had already decided entirely in their favor against the Lacedaemonians, while Menalcidas utterly deceived the Lacedaemonians by saying that the Romans had freed them completely from political union with the Achaeans.