Research Notes:

Eusebius relates a marriage of Mithridates II of Pontus and Laodice, sister of Seleucus II (Porphyr.: FGrHist. 260 F 32. 6 = Euseb. Chron. I. 251 Schoene = 118 Kaerst). This wedding was mentioned later by Mithridates VI Eupator in his speech on the eve of the First Mithridatic war. He said that the region of Greater Phrygia had been given to the Pontic king by Seleucus II Callinicus as a dowry (Justin XXXVIII. 5. 3). Eusebius also testifies that the army of Seleucus II was defeated in a battle of Ancyra by the combined forces of the Galatians, Mithridates II and Antiochus Hierax, brother of Seleucus Callinicus, after which Hierax passed through Greater Phrygia in order to collect tribute from its inhabitants (Porphyr.: FGrHist. 260 F 32. 8 = Euseb. Chron. I. 251 Schoene).

Scholars estimate in different ways the sequence and course of events along with their significance and date. One view holds that the marriage of Mithridates II and Laodice took place in 245 BC, but the king of Pontus very soon took the side of Antiochus Hierax, rebel brother of Seleucus II. According to this view, Mithridates II fell under the influence of Laodice's mother as well as of his own spouse who were both trying to help Hierax and his supporters. Another point of view holds that Mithridates II instigated the conflict between the brothers, because he was trying to exploit their struggle to weaken the Seleucid Empire and strengthen the power of Pontus at its expense....

Th. Reinach put forward an attractive suggestion: in 241 BC, Mithridates II and the Galatians, who had been allied since their common action against Ptolemy III, sided with Antiochus Hierax in the internecine war with Seleucus Callinicus, and together defeated him at the battle of Ancyra. Seleucus then managed to tempt Mithridates over to his side by marrying his sister to him and by promising to give him Greater Phrygia. This had happened in 241-239 BC, and the desertion of Hierax by the Pontic king could have been caused by a real feeling that he did not meet his expectations as co-regent and governor of Seleucus II since 245 BC. Instead of handing over to Pontus Phrygia or even part of it, Antiochus Hierax began to rule there himself, and demand tribute from its population.... ¹