Passage 8.6.6
ἡ δὲ ὑπολειπομένη τῶν ὁδῶν στενωτέρα ἐστὶ τῆς προτέρας καὶ ἄγει διὰ τοῦ Ἀρτεμισίου. τούτου δὲ ἐπεμνήσθην καὶ ἔτι πρότερον τοῦ ὄρους, ὡς ἔχοι μὲν ναὸν καὶ ἄγαλμα Ἀρτέμιδος, ἔχοι δὲ καὶ τοῦ Ἰνάχου τὰς πηγάς. ὁ δὲ Ἴναχος ἐφʼ ὅσον μὲν πρόεισι κατὰ τὴν ὁδὸν τὴν διὰ τοῦ ὄρους, τοῦτό ἐστιν Ἀργείοις καὶ Μαντινεῦσιν ὅρος τῆς χώρας· ἀποστρέψας δὲ ἐκ τῆς ὁδοῦ τὸ ὕδωρ διὰ τῆς Ἀργείας ἤδη τὸ ἀπὸ τούτου κάτεισι, καὶ ἐπὶ τούτῳ τὸν Ἴναχον ἄλλοι τε καὶ Αἰσχύλος ποταμὸν καλοῦσιν Ἀργεῖον.
The remaining road is narrower than the one previously described, and leads through Mount Artemision. I previously mentioned this mountain as having a temple and statue of Artemis, and also the sources of the Inachos. As the Inachos flows down along the road through the mountain, it forms the boundary between the lands of the Argives and the Mantineans. But from the point at which the water diverges from the road, it descends exclusively through Argive territory. Therefore, from this place onward, Aischylos, among others, calls the Inachos an Argive river.