Differences had already for several years existed between Rome and Samnium in consequence of the continual aggressions in which the Romans indulged on the Liris, and of which the founding of Fregellae in 426 was the latest and most important. But it was the Greeks of Campania that gave occasion to the outbreak of the contest. After Cumae and Capua had become Roman, nothing so naturally suggested itself to the Romans as the subjugation of the Greek city Neapolis, which ruled also over the Greek islands in the bay - the only town not yet reduced to subjection within the field of the Roman power. The Tarentines and Samnites, informed of the scheme of the Romans to obtain possession of the town, resolved to anticipate them; and while the Tarentines were too remiss perhaps rather than too distant for the execution of this plan, the Samnites actually threw into it a strong garrison. The Romans immediately declared war nominally against the Neapolitans, really against the Samnites (427), and began the siege of Neapolis. After it had lasted a while, the Campanian Greeks became weary of the disturbance of their commerce and of the foreign garrison; and the Romans, whose whole efforts were directed to keep states of the second and third rank by means of separate treaties aloof from the coalition which was about to be formed, hastened, as soon as the Greeks consented to negotiate, to offer them the most favourable terms - full equality of rights and exemption from land service, equal alliance and perpetual peace. Upon these conditions, after the Neapolitans had rid themselves of the garrison by stratagem, a treaty was concluded (428).

The Sabellian towns to the south of the Volturnus, Nola, Nuceria, Herculaneum, and Pompeii, took part with Samnium in the beginning of the war; but their greatly exposed situation and the machinations of the Romans - who endeavoured to bring over to their side the optimate party in these towns by all the levers of artifice and self-interest, and found a powerful support to their endeavours in the precedent of Capua - induced these towns to declare themselves either in favour of Rome or neutral not long after the fall of Neapolis.

A still more important success befell the Romans in Lucania. There also the people with true instinct was in favour of joining the Samnites; but, as an alliance with the Samnites involved peace with Tarentum and a large portion of the governing lords of Lucania were not disposed to suspend their profitable pillaging expeditions, the Romans succeeded in concluding an alliance with Lucania - an alliance which was invaluable, because it provided employment for the Tarentines and thus left the whole power of Rome available against Samnium.

Thus Samnium stood on all sides unsupported; excepting that some of the eastern mountain districts sent their contingents. In the year 428 the war began within the Samnite land itself: some towns on the Campanian frontier, Rufrae (between Venafrum and Teanum) and Allifae, were occupied by the Romans. In the following years the Roman armies penetrated Samnium, fighting and pillaging, as far as the territory of the Vestini, and even as far as Apulia, where they were received with open arms; everywhere they had very decidedly the advantage. The courage of the Samnites was broken; they sent back the Roman prisoners, and along with them the dead body of the leader of the war party, Brutulus Papius, who had anticipated the Roman executioners, when the Samnite national assembly determined to ask the enemy for peace and to procure for themselves more tolerable terms by the surrender of their bravest general. But when the humble, almost suppliant, request was not listened to by the Roman people (432), the Samnites, under their new general Gavius Pontius, prepared for the utmost and most desperate resistance. The Roman army, which under the two consuls of the following year (433) Spurius Postumius and Titus Veturius was encamped near Calatia (between Caserta and Maddaloni), received accounts, confirmed by the affirmation of numerous captives, that the Samnites had closely invested Luceria, and that that important town, on which depended the possession of Apulia, was in great danger. They broke up in haste. If they wished to arrive in good time, no other route could be taken than through the midst of the enemy's territory - where afterwards, in continuation of the Appian Way, the Roman road was constructed from Capua by way of Beneventum to Apulia. This route led, between the present villages of Arpaja and Montesarchio (Caudium), through a watery meadow, which was wholly enclosed by high and steep wooded hills and was only accessible through deep defiles at the entrance and outlet. Here the Samnites had posted themselves in ambush. The Romans, who had entered the valley unopposed, found its outlet obstructed by abattis and strongly occupied; on marching back they saw that the entrance was similarly closed, while at the same time the crests of the surrounding mountains were crowned by Samnite cohorts. They perceived, when it was too late, that they had suffered themselves to be misled by a stratagem, and that the Samnites awaited them, not at Luceria, but in the fatal pass of Caudium. They fought, but without hope of success and without earnest aim; the Roman army was totally unable to manoeuvre and was completely vanquished without a struggle. The Roman generals offered to capitulate. It is only a foolish rhetoric that represents the Samnite general as shut up to the simple alternatives of disbanding or of slaughtering the Roman army; he could not have done better than accept the offered capitulation and make prisoners of the hostile army - the whole force which for the moment the Roman community could bring into action - with both its commanders-in-chief. In that case the way to Campania and Latium would have stood open; and in the then existing state of feeling, when the Volsci and Hernici and the larger portion of the Latins would have received him with open arms, the political existence of Rome would have been in serious danger. But instead of taking this course and concluding a military convention, Gavius Pontius thought that he could at once terminate the whole quarrel by an equitable peace; whether it was that he shared that foolish longing of the confederates for peace, to which Brutulus Papius had fallen a victim in the previous year, or whether it was that he was unable to prevent the party which was tired of the war from spoiling his unexampled victory.  The terms laid down were moderate enough; Rome was to raze the fortresses which she had constructed in defiance of the treaty - Cales and Fregellae - and to renew her equal alliance with Samnium. After the Roman generals had agreed to these terms and had given six hundred hostages chosen from the cavalry for their faithful execution - besides pledging their own word and that of all their staff-officers on oath to the same effect - the Roman army was dismissed uninjured, but disgraced; for the Samnite army, drunk with victory, could not resist the desire to subject their hated enemies to the disgraceful formality of laying down their arms and passing under the yoke.

But the Roman senate, regardless of the oath of their officers and of the fate of the hostages, cancelled the agreement, and contented themselves with surrendering to the enemy those who had concluded it as personally responsible for its fulfilment. Impartial history can attach little importance to the question whether in so doing the casuistry of Roman advocates and priests kept the letter of the law, or whether the decree of the Roman senate violated it; under a human and political point of view no blame in this matter rests upon the Romans. It was a question of comparative indifference whether, according to the formal state law of the Romans, the general in command was or was not entitled to conclude peace without reserving its ratification by the burgesses. According to the spirit and practice of the constitution it was quite an established principle that in Rome every state-agreement, not purely military, pertained to the province of the civil authorities, and a general who concluded peace without the instructions of the senate and the burgesses exceeded his powers. It was a greater error on the part of the Samnite general to give the Roman generals the choice between saving their army and exceeding their powers, than it was on the part of the latter that they had not the magnanimity absolutely to repel such a suggestion; and it was right and necessary that the Roman senate should reject such an agreement. A great nation does not surrender what it possesses except under the pressure of extreme necessity: all treaties making concessions are acknowledgments of such a necessity, not moral obligations. If every people justly reckons it a point of honour to tear to pieces by force of arms treaties that are disgraceful, how could honour enjoin a patient adherence to a convention like the Caudine to which an unfortunate general was morally compelled, while the sting of the recent disgrace was keenly felt and the vigour of the nation subsisted unimpaired?