[A] project that was necessarily undertaken as soon as Antiochos succeeded to the kingship was to find a bride for the new king. This task was allotted to Diognetos, who later career included the command of the Seleukid navy. He was, in fact, probably one of the officials who could be used for any policy purpose; in this case he became a diplomat. A wife had suddenly become a political and diplomatic necessity. Antiochos was the last living male in the direct line of descent from Seleukos I; unless he was married swiftly, and produced a son as rapidly as possible, the dynasty might expire.... Diognetos in fact found a suitable girl, Laodike, the daughter of King Mithradates II of Pontos, though it is not known if Diognetos had much of a choice. The number of eligible and nubile princesses was suddenly rather limited, and in fact Laodike may have been the only one available. She was in fact another cousin of the king, her mother being Laodike the daughter of Antiochos II (and so sister of Seleukos II) who married Mithridates II a generation earlier.
Diognetos' mission may have been urgent from the Seleukid dynastic point of view, but in Pontos the problem was probably seen in a different light. A royal marriage required careful and serious negotiations, and this one required that some sort of stability must exist in the Seleukid kingdom before Mithradates would allow his daughter ... to be married there. Assuming that Diognetos' mission began relatively quickly after Antiochos' accession, he will have reached the Pontic court fairly early in 222, but would know by then that the kingdom he was representing was disrupted by a new civil war. The marriage negotiations were likely put on hold for the rest of the year.
In fact it may well have been news of Diognetos' mission which was the stimulus for the civil war. If he succeeded in negotiating a marriage quickly, the dynasty was halfway to safety.... For an ambitious man who felt he could be a better king than an untried boy, the likelihood of a royal marriage was a starting gun for intrigue and rebellion. Akhaios had already made his choice; Hermeias as a Karian was hardly eligible for the kingship; but Molon was probably of Macedonian descent, with a large part of the Seleukid army under his command, and was governing nearly half the kingdom. He felt he had a good, and indeed a unique, opportunity in the next year....
The position at the end of 222 ... was that in Asia Minor Akhaios had been successful in driving Attalos back to Pergamon, but was still at war with him; in the east Molon was facing the threat of attack by the army commanded by Xenon and Theodotos; in Syria Hermeias was working to persuade Antiochos to attack Ptolemy....
Preparations for war [against Ptolemaic Egypt] were set in train.... Meanwhile the marriage negotiations had succeeded. The apparently decisive actions of Akhaios in Asia Minor and in confronting Molon had obviously persuaded Mithradates that all was well, and Diognetos had escorted Laodike to Syria. Bride and groom met at Seleukeia-Zeugma on the Euphrates, which suggests that she had travelled by land through Kappadokia — another kingdom with a Seleukid queen. The marriage took place at once, with the appropriate splendour, and no doubt much publicity. The bride was then taken to Antioch, again a publicity gesture. The message was that the king was married, had allies, and the kingdom was heading for dynastic safety. 1
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