The Battle of the Plane Tree Pass took place during the Fourth Syrian War, between the Seleucid Empire under Antiochus III the Great and Ptolemaic Egypt. Most of the fighting in this war involved sieges, as Antiochus captured a series of Ptolemaic strongpoints. The battle of the Plane Tree Pass was one of the few field engagements of the war, and came while Antiochus was advancing down the Phoenicia coast.
Ptolemy IV had entrusted the defense of Coele-Syria to Nicolaus, an Aetolian general. He had been reinforced by a fleet containing 30 warships under the command of the admiral Perigenes. They attempted to stop Antiochus between Berytus and Sidon, where the width of the coastal plain was reduced by Mount Libanus. Nicolaus created a strong defensive position between the slopes of the mountain and the coast, while the fleet came as close as possible to the shore to present a continuous defensive line.
Antiochus made a four-pronged assault on the Egyptian line. He too was supported by a fleet, under the command of Diognetus, which engaged the Egyptian fleet. On land he split his army into three wings, one to attack along the beach, one across the rocky land between the beach and the mountain and one along the foot of the mountain itself. This last force was entrusted to Theodotus, a former Egyptian general who had changed sides, apparently after a failed assassination attempt on the part of Ptolemy. It was this force that won the battle. While the bulk of the Seleucid army could not make progress against the Egyptian defensive lines, Theodotus was able to break through close to the mountain.
This now placed him in a very strong position, above the Egyptian line, and he took advantage of it, charging the main Egyptian position from above. Outflanked, the Egyptian line crumbled and fled back to the safety of Sidon. Polybius reports the Egyptian losses as 2,000 killed and 2,000 captured. Seeing the defeat of the army, Perigenes called off the sea battle, which was still undecided, and the fleet escaped to Sidon.
In the aftermath of the battle, Antiochus continued his policy of capturing Egyptian held cities in Coele-Syria. This eventually gave Ptolemy and his advisors time to raise a strong army. The following year that new army would inflict a serious defeat on Antiochus at the battle of Raphia (22 June 217). All of his careful efforts in Coele-Syria would go to waste.