The long and difficult ascent was disputed by the enemy the whole way, and something like a pitched battle was fought at the top; but Antiochus persevered, and, though his army must have suffered severely, descended into Hyrcanian and captured several of the towns.
Here our main authority, Polybius, suddenly deserts us, and we can give no further account of the war beyond its general result--Artabanus and the Parthians remained unsubdued after a struggle which seems to have lasted some years; Artabanus himself displayed great valor; and at length the Syrian monarch thought it best to conclude a peace with him, in which he acknowledged the Parthian independence.

It is probable that he exacted in return a pledge that the Parthian monarch should lend him his assistance in the expedition which he was bent on conducting against Bactria; but there is no actual proof that the conditions of peace contained this clause.

We are left in doubt whether Artabanus stood aloof in the war which Antiochus waged with Euthydemus of Bactria immediately after the close of his Parthian campaigns, or whether he lent his aid to the attempt made to crush his neighbor.

Perhaps, on the whole, it is most probable that, nominally, he was Antiochus's ally in the war, but that, practically, he gave him little help, having no wish to see Syria aggrandized.
At any rate, whether Euthydemus had to meet the attack of Syria only, or of Syria and Parthia in combination, the result was, that Bactria, like Parthia, proved strong enough to maintain her ground, and that the Syrian King, after a while, grew tired of the struggle, and consented to terms of accommodation.

The Bactrian monarchy, like the Parthian, came out of the contest unscathed--indeed we may go further, and say that the position of the two kingdoms was improved by the attacks made upon them.
If a prince possessing the personal qualities that distinguished the third Antiochus, and justified the title of "Great" which he derived from his oriental expedition--if such a prince, enjoying profound peace at home, and directing the whole force of his empire against them, could not succeed in reducing to subjection the revolted provinces of the northeast, but, whatever military advantages he might gain, found conquest impossible, and returned home, having acknowledged as independent kings those whom he went out to chastise as rebellious satraps, it was evident that the kingdoms might look upon themselves as firmly established, or, at least, as secure from the danger of re-absorption into the Syrian State.