After a gap of more than 50 years for which there is little documentation, information about Seleucid activity in the battlefield becomes available again with Polybius' account of the decisive battle against Molon (5.48.17–54), which opens a series of battle accounts covering Antiochus Ill's reign.

Molon, the satrap of Media, revolted in 222 B.C. shortly after Antiochus Ill's accession, crowned himself king, and took possession of all the eastern satrapies. Antiochus, who at first concentrated his efforts on the southern frontier, contented himself with sending relatively small expeditions under second-rank generals to prevent Molon from occupying Babylonia (Polyb. 5.41–2, 5, 43.5–45.7, 46.6–48.16). But when the various expeditions had all been defeated, and Molon had taken control of much of Mesopotamia, Antiochus himself was compelled to assemble all the royal troops and lead them in a decisive confrontation with the rebel.

At the beginning of the campaign Molon was in winter quarters near Seleucia-upon-the-Tigris (48.15–16, 52.6). Antiochus marched swiftly across Mesopotamia and arrived at Apollonia, identified as Baradan Tepe, close to the junction of the Diala and the Narin Tchai (see Map 4). Molon was informed too late about Antiochus' drive, and, decamping in haste, set out for the hilly region of Apollonitis on his way to Media.

Some of the strategy of both sides is outlined by Polybius. Antiochus was eager to block Molon's way back to Media, which passed through Apollonitis, and was anxious to control this fertile region, which would give him a firm logistic base if Molon tried to play for time (51.8–11).