After the suppression of Molon's revolt, Antiochus III diverted his attention to the Ptolemaic frontier in his bid to occupy Coilē-Syria. Polybius devotes to these efforts a considerable part of the Asian section in the fifth book. After two abortive attempts to break through the Ptolemaic forts guarding the Marsyas Valley, the central route from Syria to Palestine, which passes between the Lebanon and Anti-Lebanon (45.1–46.5, 61.3–62.6), he chose the more difficult, coastal route. The narrow pass and the steep cliffs that extend in several places almost to the water-line could be easily defended by the Ptolemies. But Antiochus was able to count on Tyre and Acre in the Ptolemies' rear, which had earlier come over to his side after the defection of Theodotus the Aetolian, the Ptolemaic mercenary-officer.

The main Ptolemaic defence was concentrated near Porphyrion, identified with the ruins in the triangle between Khan Nebi Younes and the villages Barja and Jiye, near Ras Nebi Younes, 25 km south of Beirut, and the battle is said to have taken place in the nearby narrow pass (see Map 6). Abel located the battle in Ras El Sadiyatt, 4–5 km to the north of Porphyrion, but Ras Nebi Younes, which is nearer Porphyrion, seems to be more suitable: Ras El Sadiyatt is 500 m to the south of the river Damouras (Damour), mentioned as the place where Antiochus camped before the battle (68.5), and, had the battle taken place nearby, it would naturally have been called after the river (cf. the fords of the river Lycus mentioned in the report of the same expedition, 68.9).