Meanwhile the Romans were capturing some strong places in Samnium and breaking the influence of the Samnite party in Lucania; they were not in a position to prevent the departure of the army led by Egnatius. When information reached Rome that the Samnites had succeeded in frustrating all the enormous efforts made to sever the southern from the northern Italians, that the arrival of the Samnite bands in Etruria had become the signal for an almost universal rising against Rome, and that the Etruscan communities were labouring with the utmost zeal to get their own forces ready for war and to take into their pay Gallic bands, every nerve was strained also in Rome; the freedmen and the married were formed into cohorts - it was felt on all hands that the decisive crisis was near. The year 458 however passed away, apparently, in armings and marchings. For the following year (459) the Romans placed their two best generals, Publius Decius Mus and the aged Quintus Fabius Rullianus, at the head of their army in Etruria, which was reinforced with all the troops that could be spared from Campania, and amounted to at least 60,000 men, of whom more than a third were full burgesses of Rome. Besides this, two reserves were formed, the first at Falerii, the second under the walls of the capital. The rendezvous of the Italians was Umbria, towards which the roads from the Gallic, Etruscan, and Sabellian territories converged; towards Umbria the consuls also moved off their main force, partly along the left, partly along the right bank of the Tiber, while at the same time the first reserve made a movement towards Etruria, in order if possible to recall the Etruscan troops from the main scene of action for the defence of their homes. The first engagement did not prove fortunate for the Romans; their advanced guard was defeated by the combined Gauls and Samnites in the district of Chiusi. But that diversion accomplished its object. Less magnanimous than the Samnites, who had marched through the ruins of their towns that they might not be absent from the chosen field of battle, a great part of the Etruscan contingents withdrew from the federal army on the news of the advance of the Roman reserve into Etruria, and its ranks were greatly thinned when the decisive battle came to be fought on the eastern declivity of the Apennines near Sentinum.
Nevertheless it was a hotly contested day. On the right wing of the Romans, where Rullianus with his two legions fought against the Samnite army, the conflict remained long undecided. On the left, which Publius Decius commanded, the Roman cavalry was thrown into confusion by the Gallic war chariots, and the legions also already began to give way. Then the consul called to him Marcus Livius the priest, and bade him devote to the infernal gods both the head of the Roman general and the army of the enemy; and plunging into the thickest throng of the Gauls he sought death and found it. This heroic deed of despair on the part of one so eminent as a man and so beloved as a general was not in vain. The fugitive soldiers rallied; the bravest threw themselves after their leader into the hostile ranks, to avenge him or to die with him; and just at the right moment the consular Lucius Scipio, despatched by Rullianus, appeared with the Roman reserve on the imperilled left wing. The excellent Campanian cavalry, which fell on the flank and rear of the Gauls, turned the scale; the Gauls fled, and at length the Samnites also gave way, their general Egnatius falling at the gate of the camp. Nine thousand Romans strewed the field of battle; but dearly as the victory was purchased, it was worthy of such a sacrifice. The army of the coalition was dissolved, and with it the coalition itself; Umbria remained in the power of the Romans, the Gauls dispersed, the remnant of the Samnites still in compact order retreated homeward through the Abruzzi. Campania, which the Samnites had overrun during the Etruscan war, was after its close re-occupied with little difficulty by the Romans. Etruria sued for peace in the following year (460); Volsinii, Perusia, Arretium, and in general all the towns that had joined the league against Rome, promised a cessation of hostilities for four hundred months.