Note 538 — Chapter LXXXVII · FROM THE COMMENCEMENT OF THE SACRED WAR TO THAT OF THE OLYNTHIAN WAR.
Reading edition
Diodor. xvi. 33. His account of the operations of Onomarchus is, as usual, very meagre—εἰς δὲ τὴν πολεμίαν ἐμβαλὼν, Θρόνιον μὲν ἐκπολιορκήσας ἐξηνδραποδίσατο, Ἀμφισσεῖς δὲ καταπληξάμενος, τὰς δ᾽ ἐν Δωριεῦσι πόλεις πορθήσας, τὴν χώραν αὐτῶν ἐδῄωσεν.
That Thronium, with Alpônus and Nikæa, were the three places which commanded the pass of Thermopylæ—and that all the three were in possession of the Phokians immediately before they were conquered by Philip of Macedon in 346 B. C.—we know from Æschines, Fals. Leg. p. 286. c. 41.
... πρέσβεις πρὸς ὑμᾶς (the Athenians) ἦλθον ἐκ Φωκέων, βοηθεῖν αὑτοῖς κελεύοντες, καὶ ἐπαγγελλόμενοι παραδώσειν Ἀλπωνὸν καὶ Θρόνιον καὶ Νίκαιαν, τὰ τῶν παρόδων τῶν εἰς Πύλας χωρία κύρια.
In order to conquer Thronium, Onomarchus must have marched through and mastered the Epiknemidian Lokrians; and though no place except Thronium is specified by Diodorus, it seems plain that Onomarchus can not have conquered Thronium alone.