In the Adriatic sea, at the entrance of which the important and long-contemplated colony of Brundisium had at length been founded before the close of the war with Carthage (510), the supremacy of Rome was from the very first decided. In the western sea Rome had been obliged to rid herself of rivals; in the eastern, the quarrels of the Hellenes themselves prevented any of the states in the Grecian peninsula from acquiring or retaining power. The most considerable of them, that of Macedonia, had through the influence of Egypt been dislodged from the upper Adriatic by the Aetolians and from the Peloponnesus by the Achaeans, and was scarcely even in a position to defend its northern frontier against the barbarians. How concerned the Romans were to keep down Macedonia and its natural ally, the king of Syria, and how closely they associated themselves with the Egyptian policy directed to that object, is shown by the remarkable offer which after the end of the war with Carthage they made to king Ptolemy III. Euergetes, to support him in the war which he waged with Seleucus II. Callinicus of Syria (who reigned 507-529) on account of the murder of Berenice, and in which Macedonia had probably taken part with the latter. Generally, the relations of Rome with the Hellenistic states became closer; the senate already negotiated even with Syria, and interceded with the Seleucus just mentioned on behalf of the Ilians with whom the Romans claimed affinity.

For a direct interference of the Romans in the affairs of the eastern powers there was no immediate need. The Achaean league, the prosperity of which was arrested by the narrow-minded coterie-policy of Aratus, the Aetolian republic of military adventurers, and the decayed Macedonian empire kept each other in check; and the Romans of that time avoided rather than sought transmarine acquisitions. When the Acarnanians, appealing to the ground that they alone of all the Greeks had taken no part in the destruction of Ilion, besought the descendants of Aeneas to help them against the Aetolians, the senate did indeed attempt a diplomatic mediation; but when the Aetolians returned an answer drawn up in their own saucy fashion, the antiquarian interest of the Roman senators by no means provoked them into undertaking a war by which they would have freed the Macedonians from their hereditary foe (about 515).

Even the evil of piracy, which was naturally in such a state of matters the only trade that flourished on the Adriatic coast, and from which the commerce of Italy suffered greatly, was submitted to by the Romans with an undue measure of patience, - a patience intimately connected with their radical aversion to maritime war and their wretched marine. But at length it became too flagrant. Favoured by Macedonia, which no longer found occasion to continue its old function of protecting Hellenic commerce from the corsairs of the Adriatic for the benefit of its foes, the rulers of Scodra had induced the Illyrian tribes - nearly corresponding to the Dalmatians, Montenegrins, and northern Albanians of the present day - to unite for joint piratical expeditions on a great scale.

With whole squadrons of their swift-sailing biremes, the veil-known "Liburnian" cutters, the Illyrians waged war by sea and along the coasts against all and sundry. The Greek settlements in these regions, the island-towns of Issa (Lissa) and Pharos (Lesina), the important ports of Epidamnus (Durazzo) and Apollonia (to the north of Avlona on the Aous) of course suffered especially, and were repeatedly beleaguered by the barbarians. Farther to the south, moreover, the corsairs established themselves in Phoenice, the most flourishing town of Epirus; partly voluntarily, partly by constraint, the Epirots and Acarnanians entered into an unnatural symmachy with the foreign freebooters; the coast was insecure even as far as Elis and Messene. In vain the Aetolians and Achaeans collected what ships they had, with a view to check the evil: in a battle on the open sea they were beaten by the pirates and their Greek allies; the corsair fleet was able at length to take possession even of the rich and important island of Corcyra (Corfu). The complaints of Italian mariners, the appeals for aid of their old allies the Apolloniates, and the urgent entreaties of the besieged Issaeans at length compelled the Roman senate to send at least ambassadors to Scodra. The brothers Gaius and Lucius Coruncanius went thither to demand that king Agron should put an end to the disorder. The king answered that according to the national law of the Illyrians piracy was a lawful trade, and that the government had no right to put a stop to privateering; whereupon Lucius Coruncanius replied, that in that case Rome would make it her business to introduce a better law among the Illyrians. For this certainly not very diplomatic reply one of the envoys was - by the king's orders, as the Romans asserted - murdered on the way home, and the surrender of the murderers was refused. The senate had now no choice left to it. In the spring of 525 a fleet of 200 ships of the line, with a landing-army on board, appeared off Apollonia; the corsair-vessels were scattered before the former, while the latter demolished the piratic strongholds; the queen Teuta, who after the death of her husband Agron conducted the government during the minority of her son Pinnes, besieged in her last retreat, was obliged to accept the conditions dictated by Rome. The rulers of Scodra were again confined both on the north and south to the narrow limits of their original domain, and had to quit their hold not only on all the Greek towns, but also on the Ardiaei in Dalmatia, the Parthini around Epidamnus, and the Atintanes in northern Epirus; no Illyrian vessel of war at all, and not more than two unarmed vessels in company, were to be allowed in future to sail to the south of Lissus (Alessio, between Scutari and Durazzo). The maritime supremacy of Rome in the Adriatic was asserted, in the most praiseworthy and durable way, by the rapid and energetic suppression of the evil of piracy.

But the Romans went further, and established themselves on the east coast. The Illyrians of Scodra were rendered tributary to Rome; Demetrius of Pharos, who had passed over from the service of Teuta to that of the Romans, was installed, as a dependent dynast and ally of Rome, over the islands and coasts of Dalmatia; the Greek cities Corcyra, Epidamnus, Apollonia, and the communities of the Atintanes and Parthini were attached to Rome under mild forms of symmachy. These acquisitions on the east coast of the Adriatic were not sufficiently extensive to require the appointment of a special auxiliary consul; governors of subordinate rank appear to have been sent to Corcyra and perhaps also to other places, and the superintendence of these possessions seems to have been entrusted to the chief magistrates who administered Italy[11]. Thus the most important maritime stations in the Adriatic became subject, like Sicily and Sardinia, to the authority of Rome. What other result was to be expected? Rome was in want of a good naval station in the upper Adriatic - a want which was not supplied by her possessions on the Italian shore; her new allies, especially the Greek commercial towns, saw in the Romans their deliverers, and doubtless did what they could permanently to secure so powerful a protection; in Greece itself no one was in a position to oppose the movement; on the contrary, the praise of the liberators was on every one's lips. It may be a question whether there was greater rejoicing or shame in Hellas, when, in place of the ten ships of the line of the Achaean league, the most warlike power in Greece, two hundred sail belonging to the barbarians now entered her harbours and accomplished at a blow the task, which properly belonged to the Greeks, but in which they had failed so miserably. But if the Greeks were ashamed that the salvation of their oppressed countrymen had to come from abroad, they accepted the deliverance at least with a good grace; they did not fail to receive the Romans solemnly into the fellowship of the Hellenic nation by admitting them to the Isthmian games and the Eleusinian mysteries. Macedonia was silent; it was not in a condition to protest in arms, and disdained to do so in words. No resistance was encountered. Nevertheless Rome, by seizing the keys to her neighbour's house, had converted that neighbour into an adversary who, should he recover his power, or should a favourable opportunity occur, might be expected to know how to break the silence. Had the energetic and prudent king Antigonus Doson lived longer, he would have doubtless taken up the gauntlet which the Romans had flung down, for, when some years afterwards the dynast Demetrius of Pharos withdrew from the hegemony of Rome, prosecuted piracy contrary to the treaty in concert with the Istrians, and subdued the Atintanes whom the Romans had declared independent, Antigonus formed an alliance with him, and the troops of Demetrius fought along with the army of Antigonus at the battle of Sellasia (532). But Antigonus died (in the winter 533-4); and his successor Philip, still a boy, allowed the Consul Lucius Aemilius Paullus to attack the ally of Macedonia, to destroy his capital, and to drive him from his kingdom into exile (535).