A consolidation of Pontus in north-western Asia Minor caused a falling-off in relations with the Galatians and Bithynia, in which Ziaelas, son of Nicomedes I, began to fight for the throne, using the support of the Tolistobogii, a Galatian tribe (Memn. XXII). Around 255-250 BC, the Galatians invaded Pontus with the support of Heraclea Pontica, its former ally (Memn. XXIV). At the same time, Antiochus II recognized the independence of Cappadocia by the marriage of his daughter Stratonice to the Cappadocian king Ariarathes II (Diod. XXXI. 19). Bearing in mind the tense relations of the Syrian king with the Galatians, enemies of Pontus, one can assume that approximately from that time on, the Seleucid kingdom began to draw closer to the kingdom of Pontus, where Mithridates II around 256 BC had succeeded Ariobarzanes (266-256 BC), son and successor of Mithridates I Ctistes....
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.
We can agree only partially with this. Polybius' evidence that Logbasis from Selga, friend and supporter of Antiochus Hierax, had brought up Laodice, daughter of Mithridates II, whose tutor he happened to be (Polyb. IV. 74. 5), can hardly refer to the late 240s BC. Laodice, daughter of Laodice, sister of Seleucus II, given in marriage to the king of Pontus at the end of "The War of Laodice", and in 240s-230s BC she was still a child. That is why she could not marry Antiochus Hierax to conclude the alliance with Pontus. It seems that Mithridates never conducted any dynastic policy in relation to Hierax. Furthermore, it is doubtful that the marriage of Mithridates II and Callinicus' sister was concluded in 245 BC, because the anti-Ptolemaic action of the Galatians together with the army of Pontus could not have taken place before 246/245 BC. If, at that time, Seleucus II had a dynastic union with Mithridates, then the Pontic king would act against the Egyptians in association with the king of Syria. But the Pontic ruler and his brother took the field with the Galatians on their own, as Seleucus at that very time began to recover from a heavy defeat and great losses, particularly of several territories within the kingdom. Before 242 BC, he could hardly have promised his new Pontic relative any kind of territorial concessions as dowry for his sister, because practically all his possessions in Asia Minor were lost. This could refer to the whole of Phrygia. For that reason the course of events should be the opposite of what modern scholars usually suggest.
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. This sundered Mithridates from Hierax and brought him into alliance with Seleucus II, who either promised Greater Phrygia to him or actually gave him a part of it. Therefore the whole Pontic policy toward the Seleucids was hardly aimed at destroying the dynastic and state basis of their power: it was specifically conducted to obtain Greater Phrygia, because it was subject to the rulers who were members of this royal dynasty. Presumably, this policy was not completely successful, as the greatest part of the country was still held by Antiochus Hierax.
But Mithridates of Pontus was trying by all means possible to keep those of his few territorial acquisitions that may have been given to him as a dowry. That is why he decided to secure himself from future attacks by Antiochus Hierax and the Galatians, now the allies of a new ruler of Asia Minor. The Pontic kingdom decided to give him his daughter, born from Laodice, a sister of Seleucus II, as a hostage or simply to bring her up at his court, because the girl was Hierax's niece (Polyb. IV. 74. 5). This gesture yielded scanty hope of preserving good terms with his former ally Antiochus Hierax, who contended with Attalus I of Pergamum for possession of Phrygia. Attalus I defeated Hierax several times, and this happened in Hellespontine Phrygia as well.... After that, the king of Pergamum enlarged his territory at the expense of Phrygia, Lydia and Lycaonia. Thus the question of handing Phrygia over to Pontus, which had been raised earlier by Seleucus II, was left unresolved, and it remained an open question in relations between the Seleucids and the Mithridatids of Pontus. 1
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