Antiochus having entered upon the eastward campaign (212-205) for which he will gain renown, now attacks Artabanus.

The Parthians may in fact be hostile to the local Greek populations: during the initial phase of the war, they massacre all the Greek inhabitants of the city of Syrinx in Hyrcania.

Antiochus takes Syrinx and Hecatompylos, the Arsacid capital (the present location of which is uncertain), then crosses the mountains separating that province from Parthia, which he occupies.

Artabanus flees and takes refuge with the friendly Apasiacae, as had his father, Arsaces I.

The conflict between the Seleucids and Parthia, however, is ended by a compromise, just as it had been at the time of the invasion of Seleucus II.

A much more important struggle against the Bactrian kingdom of Euthydemus awaits Antiochus.

Preferred to make peace with Artabanus, he accords him the title of king in exchange for recognition of his fealty, and obliges the Parthian to send troops to reinforce the Syrian army.

This safeguards the rear of the Seleucid king, but the Macedonians have definitively lost the two provinces held by Artabanus.