Elated by his success and wishing to overawe and intimidate the barbarous princes whose dominions bordered on and lay beyond his own provinces, so as to prevent their furnishing anyone who rebelled against him with supplies or armed assistance, the king decided to march against them and in the first place against Artabarzanes,
who was considered the most important and energetic of these potentates, being master of the so‑called satrapies and the tribes on their borders.
But Hermeias at that time was afraid of an expedition into the interior owing to its danger and continued to yearn for the campaign against Ptolemy which he had originally planned.
When, however, the news came that a son had been born to Antiochus, thinking that possibly in the interior Antiochus might meet with some misfortune at the hands of the barbarians and give him the opportunity of compassing his death, he gave his consent to the expedition, feeling sure
that if he could put Antiochus out of the way he would be himself the child's guardian and master of the kingdom.
The campaign once decided on, they crossed the river Zagrus
into the territory of Artabarzanes which borders on <a class="linkToPlace" target="_blank" href="/place?placename=Media&groupId=742&placeId=1354">Media</a>, from which it is separated by the intervening chain of mountains. Above it lies that part of <a class="linkToPlace" target="_blank" href="/place?placename=Pontus&groupId=910&placeId=1634">Pontus</a> which descends to the river <a class="linkToPlace" target="_blank" href="/place?placename=Phasis&groupId=882&placeId=1590">Phasis</a>. It reaches as far as the Caspian Sea
and has a large and warlike population chiefly mounted, while its natural resources provide every kind of warlike material.
The principality still remains under Persian rule, having been overlooked in the time of Alexander.
Artabarzanes, terror-struck at the king's attack, chiefly owing to his years as he was quite an old man, yielded to circumstances and made terms which satisfied Antiochus.
Walbank Commentary