The next neighbours and kinsmen of the Senones, the Boii, terrified and exasperated by a catastrophe which had been accomplished with so fearful a rapidity, united instantaneously with the Etruscans, who still continued the war, and whose Senonian mercenaries now fought against the Romans no longer as hirelings, but as desperate avengers of their native land. A powerful Etrusco-Gallic army marched against Rome to retaliate the annihilation of the Senonian tribe on the enemy's capital, and to extirpate Rome from the face of the earth more completely than had been formerly done by the chieftain of these same Senones. But the combined army was decidedly defeated by the Romans at its passage of the Tiber in the neighbourhood of the Vadimonian lake (471). After they had once more in the following year risked a general engagement near Populonia with no better success, the Boii deserted their confederates and concluded a peace on their own account with the Romans (472). Thus the Gauls, the most formidable member of the league, were conquered in detail before the league was fully formed, and by that means the hands of Rome were left free to act against Lower Italy, where during the years 469-471 the contest had not been carried on with any vigour. Hitherto the weak Roman army had with difficulty maintained itself in Thurii against the Lucanians and Bruttians; but now (472) the consul Gaius Fabricius Luscinus appeared with a strong army in front of the town, relieved it, defeated the Lucanians in a great engagement, and took their general Statilius prisoner. The smaller non-Doric Greek towns, recognizing the Romans as their deliverers, everywhere voluntarily joined them. Roman garrisons were left behind in the most important places, in Locri, Croton, Thurii, and especially in Rhegium, on which latter town the Carthaginians seem also to have had designs. Everywhere Rome had most decidedly the advantage. The annihilation of the Senones had given to the Romans a considerable tract of the Adriatic coast. With a view, doubtless, to the smouldering feud with Tarentum and the already threatened invasion of the Epirots, they hastened to make themselves sure of this coast as well as of the Adriatic sea. A burgess colony was sent out (about 471) to the seaport of Sena (Sinigaglia), the former capital of the Senonian territory; and at the same time a Roman fleet sailed from the Tyrrhene sea into the eastern waters, manifestly for the purpose of being stationed in the Adriatic and of protecting the Roman possessions there.
The Tarentines since the treaty of 450 had lived at peace with Rome. They had been spectators of the long struggle of the Samnites, and of the rapid extirpation of the Senones; they had acquiesced without remonstrance in the establishment of Venusia, Atria, and Sena, and in the occupation of Thurii and of Rhegium. But when the Roman fleet, on its voyage from the Tyrrhene to the Adriatic sea, now arrived in the Tarentine waters and cast anchor in the harbour of the friendly city, the long, cherished resentment at length overflowed. Old treaties, which prohibited the war-vessels of Rome from sailing to the east of the Lacinian promontory, were appealed to by popular orators in the assembly of the citizens. A furious mob fell upon the Roman ships of war, which, assailed suddenly in a piratical fashion, succumbed after a sharp struggle; five ships were taken and their crews executed or sold into slavery; the Roman admiral himself had fallen in the engagement. Only the supreme folly and supreme unscrupulousness of mob-rule can account for those disgraceful proceedings. The treaties referred to belonged to a period long past and forgotten; it is clear that they no longer had any meaning, at least subsequently to the founding of Atria and Sena, and that the Romans entered the bay on the faith of the existing alliance; indeed, it was very much their interest - as the further course of things showed - to afford the Tarentines no sort of pretext for declaring war. In declaring war against Rome - if such was their wish - the statesmen of Tarentum were only doing what they should have done long before; and if they preferred to rest their declaration of war upon the formal pretext of a breach of treaty rather than upon the real ground, no further objection could be taken to that course, seeing that diplomacy has always reckoned it beneath its dignity to speak the plain truth in plain language. But to make an armed attack upon the fleet without warning, instead of summoning the admiral to retrace his course, was a foolish no less than a barbarous act - one of those horrible barbarities of civilization, when moral principle suddenly forsakes the helm and the merest coarseness emerges in its room, as if to warn us against the childish belief that civilization is able to extirpate brutality from human nature.
And, as if what they had done had not been enough, the Tarentines after this heroic feat attacked Thurii, the Roman garrison of which capitulated in consequence of the surprise (in the winter of 472-473); and inflicted: severe chastisement on the Thurines - the same, whom Tarentine policy had abandoned to the Lucanians and thereby forcibly constrained into surrender to Rome - for their desertion from the Hellenic party to the barbarians.
The barbarians, however, acted with a moderation which, considering their power and the provocation they had received, excites astonishment. It was the interest of Rome to maintain as long as possible the Tarentine neutrality, and the leading men in the senate accordingly rejected the proposal, which a minority had with natural resentment submitted, to declare war at once against the Tarentines. In fact, the continuance of peace on the part of Rome was proffered on the most moderate terms consistent with her honour - the release of the captives, the restoration of Thurii, the surrender of the originators of the attack on the fleet. A Roman embassy proceeded with these proposals to Tarentum (473), while at the same time, to add weight to their words, a Roman army under the consul Lucius Aemilius advanced into Samnium. The Tarentines could, without forfeiting aught of their independence, accept these terms; and considering the little inclination for war in so wealthy a commercial city, the Romans had reason to presume that an accommodation was still possible. But the attempt to preserve peace failed, whether through the opposition of those Tarentines who recognized the necessity of meeting the aggressions of Rome, the sooner the better, by a resort to arms, or merely through the unruliness of the city rabble, which with characteristic Greek naughtiness subjected the person of the envoy to an unworthy insult. The consul now advanced into the Tarentine territory; but instead of immediately commencing hostilities, he offered once more the same terms of peace; and, when this proved in vain, he began to lay waste the fields and country houses, and he defeated the civic militia. The principal persons captured, however, were released without ransom; and the hope was not abandoned that the pressure of war would give to the aristocratic party ascendency in the city and so bring about peace. The reason of this reserve was, that the Romans were unwilling to drive the city into the arms of the Epirot king. His designs on Italy were no longer a secret. A Tarentine embassy had already gone to Pyrrhus and returned without having accomplished its object. The king had demanded more than it had powers to grant. It was necessary that they should come to a decision. That the civic militia knew only how to run away from the Romans, had been made sufficiently clear. There remained only the choice between a peace with Rome, which the Romans still were ready to agree to on equitable terms, and a treaty with Pyrrhus on any condition that the king might think proper; or, in other words, the choice between submission to the supremacy of Rome, and subjection to the tyrannis of a Greek soldier.