For the protection of the east coast he relied partly on the orders which he had given for the laying waste of the islands of Sciathus and Peparethus, which might have furnished a station to the enemy's fleet, partly on the garrisoning of Thasos and the coast and on the fleet organized at Demetrias under Heraclides.

For the south frontier be had been obliged to reckon solely upon the more than doubtful neutrality of the Aetolians.

These now suddenly joined the league against Macedonia, and immediately in conjunction with the Athamanes penetrated into Thessaly, while simultaneously the Dardani and Illyrians overran the northern provinces, and the Roman fleet under Lucius Apustius, departing from Corcyra, appeared in the eastern waters, where the ships of Attalus, the Rhodians, and the Istrians joined it.
Philip, on learning this, voluntarily abandoned his position and retreated in an easterly direction: whether he did so in order to repel the probably unexpected invasion of the Aetolians, or to draw the Roman army after him with a view to its destruction, or to take either of these courses according to circumstances, cannot well be determined.

He managed his retreat so dexterously that Galba, who adopted the rash resolution of following him, lost his track, and Philip was enabled to reach by a flank movement, and to occupy, the narrow pass which separates the provinces of Lyncestis and Eordaea, with the view of awaiting the Romans and giving them a warm reception there.

A battle took place on the spot which he had selected; but the long Macedonian spears proved unserviceable on the wooded and uneven ground.