Passage 8.29.1
διαβάντων δὲ Ἀλφειὸν χώρα τε καλουμένη Τραπεζουντία καὶ πόλεώς ἐστιν ἐρείπια Τραπεζοῦντος. καὶ αὖθις ἐπὶ τὸν Ἀλφειὸν ἐν ἀριστερᾷ καταβαίνοντι ἐκ Τραπεζοῦντος, οὐ πόρρω τοῦ ποταμοῦ Βάθος ἐστὶν ὀνομαζόμενον, ἔνθα ἄγουσι τελετὴν διὰ ἔτους τρίτου θεαῖς Μεγάλαις· καὶ πηγή τε αὐτόθι ἐστὶν Ὀλυμπιὰς καλουμένη, τὸν ἕτερον τῶν ἐν αὐτῶν οὐκ ἀπορρέουσα, καὶ πλησίον τῆς πηγῆς πῦρ ἄνεισι. λέγουσι δὲ οἱ Ἀρκάδες τὴν λεγομένην γιγάντων μάχην καὶ θεῶν ἐνταῦθα καὶ οὐκ ἐν τῇ Θρᾳκίᾳ γενέσθαι Παλλήνῃ, καὶ θύουσιν ἀστραπαῖς αὐτόθι καὶ θυέλλαις τε καὶ βρονταῖς.
After crossing the Alpheios, there is a region called Trapezountia and the ruins of a city, Trapezous. Proceeding again toward the Alpheios, descending from Trapezous on the left, not far from the river is a place called Bathos. There every third year they hold rites in honor of the Great Goddesses. At this place there is also a spring called Olympias, whose water flows only every other year, and near the spring, fire emerges from the ground. The Arcadians say that the battle between Giants and gods occurred here rather than at Pallene in Thrace, and here they make offerings to lightning, storms, and thunder.