When Philip concluded his treaty with the Aetolians and Romans in 548-9, he seriously intended to make a lasting peace with Rome, and to devote himself exclusively in future to the affairs of the east. It admits of no doubt that he saw with regret the rapid subjugation of Carthage; and it may be, that Hannibal hoped for a second declaration of war from Macedonia, and that Philip secretly reinforced the last Carthaginian army with mercenaries[2]. But the tedious affairs in which he had meanwhile involved himself in the east, as well as the nature of the alleged support, and especially the total silence of the Romans as to such a breach of the peace while they were searching for grounds of war, place it beyond doubt, that Philip was by no means disposed in 551 to make up for what he ought to have done ten years before. He had turned his eyes to an entirely different quarter. Ptolemy Philopator of Egypt had died in 549. Philip and Antiochus, the kings of Macedonia and Asia, had combined against his successor Ptolemy Epiphanes, a child of five years old, in order completely to gratify the ancient grudge which the monarchies of the mainland entertained towards the maritime state. The Egyptian state was to be broken up; Egypt and Cyprus were to fall to Antiochus Cyrene, Ionia, and the Cyclades to Philip. Thoroughly after the manner of Philip, who ridiculed such considerations, the kings began the war not merely without cause but even without pretext, "just as the large fishes devour the small". The allies, moreover, had made their calculations correctly, especially Philip. Egypt had enough to do in defending herself against the nearer enemy in Syria, and was obliged to leave her possessions in Asia Minor and the Cyclades undefended when Philip threw himself upon these as his share of the spoil. In the year in which Carthage concluded peace with Rome (553), Philip ordered a fleet equipped by the towns subject to him to take on board troops, and to sail along the coast of Thrace. There Lysimachia was taken from the Aetolian garrison, and Perinthus, which stood in the relation of clientship to Byzantium, was likewise occupied. Thus the peace was broken as respected the Byzantines; and as respected the Aetolians, who had just made peace with Philip, the good understanding was at least disturbed. The crossing to Asia was attended with no difficulties, for Prusias king of Bithynia was in alliance with Macedonia. By way of recompense, Philip helped him to subdue the Greek mercantile cities in his territory. Chalcedon submitted. Cius, which resisted, was taken by storm and levelled with the ground, and its inhabitants were reduced to slavery - a meaningless barbarity, which annoyed Prusias himself who wished to get possession of the town uninjured, and which excited profound indignation throughout the Hellenic world. The Aetolians, whose strategus had commanded in Cius, and the Rhodians, whose attempts at mediation had been contemptuously and craftily frustrated by the king, were especially offended.

But even had this not been so, the interests of all Greek commercial cities were at stake. They could not possibly allow the mild and almost purely nominal Egyptian rule to be supplanted by the Macedonian despotism, with which urban self-government and freedom of commercial intercourse were not at all compatible; and the fearful treatment of the Cians showed that the matter at stake was not the right of confirming the charters of the towns, but the life or death of one and all. Lampsacus had already fallen, and Thasos had been treated like Cius; no time was to be lost. Theophiliscus, the vigilant strategusof Rhodes, exhorted his citizens to meet the common danger by common resistance, and not to suffer the towns and islands to become one by one a prey to the enemy. Rhodes resolved on its course, and declared war against Philip. Byzantium joined it; as did also the aged Attalus king of Pergamus, personally and politically the enemy of Philip. While the fleet of the allies was mustering on the Aeolian coast, Philip directed a portion of his fleet to take Chios and Samos. With the other portion he appeared in person before Pergamus, which however he invested in vain; he had to content himself with traversing the level country and leaving the traces of Macedonian valour on the temples which he destroyed far and wide. Suddenly he departed and re-embarked, to unite with his squadron which was at Samos. But the Rhodo-Pergamene fleet followed him, and forced him to accept battle in the straits of Chios. The number of the Macedonian decked vessels was smaller, but the multitude of their open boats made up for this inequality, and the soldiers of Philip fought with great courage. But he was at length defeated. Almost half of his decked vessels, 24 sail, were sunk or taken; 6000 Macedonian sailors and 3000 soldiers perished, amongst whom was the admiral Democrates; 2000 were taken prisoners. The victory cost the allies no more than 800 men and six vessels. But, of the leaders of the allies, Attalus had been cut off from his fleet and compelled to let his own vessel run aground at Erythrae; and Theophiliscus of Rhodes, whose public spirit had decided the question of war and whose valour had decided the battle, died on the day after it of his wounds. Thus while the fleet of Attalus went home and the Rhodian fleet remained temporarily at Chios, Philip, who falsely ascribed the victory to himself, was able to continue his voyage and to turn towards Samos, in order to occupy the Carian towns. On the Carian coast the Rhodians, not on this occasion supported by Attalus, gave battle for the second time to the Macedonian fleet under Heraclides, near the little island of Lade in front of the port of Miletus. The victory, claimed again by both sides, appears to have been this time gained by the Macedonians; for while the Rhodians retreated to Myndus and thence to Cos, the Macedonians occupied Miletus, and a squadron under Dicaearchus the Aetolian occupied the Cyclades. Philip meanwhile prosecuted the conquest of the Rhodian possessions on the Carian mainland, and of the Greek cities: had he been disposed to attack Ptolemy in person, and had he not preferred to confine himself to the acquisition of his own share in the spoil, he would now have been able to think even of an expedition to Egypt. In Caria no army confronted the Macedonians, and Philip traversed without hindrance the country from Magnesia to Mylasa; but every town in that country was a fortress, and the siege-warfare was protracted without yielding or promising any considerable results. Zeuxis the satrap of Lydia supported the ally of his master with the same lukewarmness as Philip had manifested in promoting the interests of the Syrian king, and the Greek cities gave their support only under the pressure of fear or force. The provisioning of the army became daily more difficult; Philip was obliged today to plunder those who but yesterday had voluntarily supplied his wants, and then he had reluctantly to submit to beg afresh. Thus the good season of the year gradually drew to an end, and in the interval the Rhodians had reinforced their fleet and had also been rejoined by that of Attalus, so that they were decidedly superior at sea. It seemed almost as if they might cut off the retreat of the king and compel him to take up winter quarters in Caria, while the state of affairs at home, particularly the threatened intervention of the Aetolians and Romans, urgently demanded his return. Philip saw the danger; he left garrisons amounting together to 3000 men, partly in Myrina to keep Pergamus in check, partly in the petty towns round Mylasa - Iassus, Bargylia, Euromus and Pedasa - to secure for him the excellent harbour and a landing place in Caria; and, owing to the negligence with which the allies guarded the sea, he succeeded in safely reaching the Thracian coast with his fleet and arriving at home before the winter of 553-4.