After his defeat at Raphia, Antiochus III concentrated on recovering Asia Minor. Having succeeded in capturing Achaeus and bringing the rebellion to an end in 214 B.C., he turned to the pursuit of his great dream: the reestablishment of the territorial dimensions of the Empire in the time of Seleucus I by means of a forceful anabasis to the east. Only a few fragments of Polybius refer to this great expedition and include some account of military operations (10.28–31, 48–9). The most interesting is the detailed description, based probably on eyewitness accounts, of the crossing of the Elburz range on the way from Hecatompylus to Hyrcania, which demonstrates the march order and tactics of Antiochus III in difficult mountain passes (28–31).

Antiochus' route has been identified as the central pass of the Elburz range leading from Shahrud through the Chalchanlyan Pass to the Chasman – Sawer valley, and from there through the Quzluq Pass to Astrabad (Gorgan, see Map 9). The main part of the route follows a riverbed which enters a narrow and precipitous gorge with cliffs soaring some 800–1200 m above the defile about 6 km from the Chalchanlyan Pass (30.2), a circumstance which led Antiochus to fear an ambush either by local tribes or Arsaces! troops. His anxiety was increased by Arsaces' reluctance to join battle, even near Hecatompylus, which was ideal for cavalry warfare, in which the Parthians obviously had a considerable advantage.