Passage 7.7.2
ἀθροίζεσθαι δὲ ἐς Αἴγιόν σφισιν ἔδοξεν· αὕτη γὰρ μετὰ Ἑλίκην ἐπικλυσθεῖσαν πόλεων ἐν Ἀχαΐᾳ τῶν ἄλλων δόξῃ προεῖχεν ἐκ παλαιοῦ καὶ ἴσχυεν ἐν τῷ τότε. Ἑλλήνων δὲ τῶν λοιπῶν Σικυώνιοι συνεδρίου πρῶτοι τοῦ Ἀχαιῶν μετέσχον, μετὰ δὲ Σικυωνίους ἐσῄεσαν ἤδη καὶ τῶν ἄλλων Πελοποννησίων οἱ μὲν αὐτίκα, οἱ δὲ χρόνον τινὰ ἐπισχόντες· τοὺς δὲ καὶ ἐκτὸς οἰκοῦντας τοῦ ἰσθμοῦ συντελεῖν ἐς Ἀχαιοὺς ἔπειθεν, ὅτι ἐς πλέον ἰσχύος προϊὸν ἑώρων ἀεὶ τὸ Ἀχαϊκόν.
They decided to gather at Aigion, for among the cities of Achaia this city had, from ancient times, held precedence in reputation above all the others after the flooding of Helike and retained its strength even then. Of the remaining Greeks, the Sikyonians were the first to take part in the Achaean assembly. After the Sikyonians, others among the Peloponnesians also joined, some immediately and others after some hesitation. Even inhabitants beyond the Isthmus were persuaded to join the Achaians, since they saw clearly that the Achaian league was continually increasing in power.