Thus began, a few months after the death of Drusus, in the winter of 663-4, the struggle - as one of the coins of the insurgents represents it - of the Sabellian ox against the Roman she-wolf. Both sides made zealous preparations: in Italia great stores of arms, provisions, and money were accumulated; in Rome the requisite supplies were drawn from the provinces and particularly from Sicily, and the long-neglected walls were put in a state of defence against any contingency. The forces were in some measure equally balanced. The Romans filled up the blanks in their Italian contingents partly by increased levies from the burgesses and from the inhabitants - already almost wholly Romanized - of the Celtic districts on the south of the Alps, of whom 10,000 served in the Campanian army alone[13], partly by the contingents of the Numidians and other transmarine nations; and with the aid of the free cities in Greece and Asia Minor they collected a war fleet[14]. On both sides, without reckoning garrisons, as many as 100,000 soldiers were brought into the field[15], and in the ability of their men, in military tactics and armament, the Italians were nowise inferior to the Romans.

The conduct of the war was very difficult both for the insurgents and for the Romans, because the territory in revolt was very extensive and a great number of fortresses adhering to Rome were scattered up and down in it: so that on the one hand the insurgents found themselves compelled to combine a siege-warfare, which broke up their forces and consumed their time, with the protection of an extended frontier; and on the other hand the Romans could not well do otherwise than combat the insurrection, which had no proper centre, simultaneously in all the insurgent districts. In a military point of view the insurgent country fell into two divisions; in the northern, which reached from Picenum and the Abruzzi to the northern border of Campania and embraced the districts speaking Latin, the chief command was held on the Italian side by the Marsian Quintus Silo, on the Roman side by Publius Rutilius Lupus, both as consuls; in the southern, which included Campania, Samnium, and generally the regions speaking Sabellian, the Samnite Gaius Papius Mutilus commanded as consul of the insurgents, and Lucius Julius Caesar as the Roman consul. With each of the two commanders-in-chief there were associated on the Italian side six, on the Roman side five, lieutenant-commanders, each of whom conducted the attack or defence in a definite district, while the consular armies were destined to act more freely and to strike the decisive blow. The most esteemed Roman officers, such as Gaius Marius, Quintus Catulus, and the two consulars of experience in the Spanish war, Titus Didius and Publius Crassus, placed themselves at the disposal of the consuls for these posts; and though the Italians had not names so celebrated to oppose to them, yet the result showed that their leaders were in a military point of view nowise inferior to the Romans.

The offensive in this thoroughly desultory war was on the whole on the side of the Romans, but was nowhere decisively assumed even on their part. It is surprising that the Romans did not collect their troops for the purpose of attacking the insurgents with a superior force, and that the insurgents made no attempt to advance into Latium and to throw themselves on the hostile capital. We are how ever too little acquainted with their respective circumstances to judge whether or how they could have acted otherwise, or to what extent the remissness of the Roman government on the one hand and the looseness of the connection among the federate communities on the other contributed to this want of unity in the conduct of the war. It is easy to see that with such a system there would doubtless be victories and defeats, but the final settlement might be very long delayed; and it is no less plain that a clear and vivid picture of such a war - which resolved itself into a series of engagements on the part of individual corps operating at the same time, sometimes separately, sometimes in combination - cannot be prepared out of the remarkably fragmentary accounts which have come down to us.

The first assault, as a matter of course, fell on the fortresses adhering to Rome in the insurgent districts, which in all haste closed their gates and carried in their moveable property from the country. Silo threw himself on the fortress designed to hold in check the Marsians, the strong Alba, Mutilus on the Latin town of Aesernia established in the heart of Samnium: in both cases they encountered the most resolute resistance. Similar conflicts probably raged in the north around Firmum, Atria, Pinna, in the south around Luceria, Beneventum, Nola, Paestum, before and while the Roman armies gathered on the borders of the insurgent country. After the southern army under Caesar had assembled in the spring of 664 in Campania which for the most part held by Rome, and had provided Capua - with its domain so important for the Roman finances - as well as the more important allied cities with garrisons, it attempted to assume the offensive and to come to the aid of the smaller divisions sent on before it to Samnium and Lucania under Marcus Marcellus and Publius Crassus. But Caesar was repulsed by the Samnites and Marsians under Publius Vettius Scato with severe loss, and the important town of Venafrum thereupon passed over to the insurgents, into whose hands it delivered its Roman garrison. By the defection of this town, which lay on the military road from Campania to Samnium, Aesernia was isolated, and that fortress already vigorously assailed found itself now exclusively dependent on the courage and perseverance of its defenders and their commandant Marcellus. It is true that an incursion, which Sulla happily carried out with the same artful audacity as formerly his expedition to Bocchus, relieved the hard-pressed Aesernians for a moment; nevertheless they were after an obstinate resistance compelled by the extremity of famine to capitulate towards the end of the year.

In Lucania too Publius Crassus was defeated by Marcus Lamponius, and compelled to shut himself up in Grumentum, which fell after a long and obstinate siege. With these exceptions, they had been obliged to leave Apulia and the southern districts totally to themselves. The insurrection spread; when Mutilus advanced into Campania at the head of the Samnite army, the citizens of Nola surrendered to him their city and delivered up the Roman garrison, whose commander was executed by the orders of Mutilus, while the men were distributed through the victorious army. With the single exception of Nuceria, which adhered firmly to Rome, all Campania as far as Vesuvius was lost to the Romans; Salernum, Stabiae, Pompeii, Herculaneum declared for the insurgents; Mutilus was able to advance into the region to the north of Vesuvius, and to besiege Acerrae with his Samnito-Lucanian army. The Numidians, who were in great numbers in Caesar's army, began to pass over in troops to Mutilus or rather to Oxyntas, the son of Jugurtha, who on the surrender of Venusia had fallen into the hands of the Samnites and now appeared among their ranks in regal purple; so that Caesar found himself compelled to send home the whole African corps. Mutilus ventured even to attack the Roman camp; but he was repulsed, and the Samnites, who while retreating were assailed in the rear by the Roman cavalry, left nearly 6000 dead on the field of battle. It was the first notable success which the Romans gained in this war; the army proclaimed the general imperator, and the sunken courage of the capital began to revive. It is true that not long afterwards the victorious army was attacked in crossing a river by Marius Egnatius, and so emphatically defeated that it had to retreat as far as Teanum and to be reorganized there; but the exertions of the active consul succeeded in restoring his army to a serviceable condition even before the arrival of winter, and he reoccupied his old position under the walls of Acerrae, which the Samnite main army under Mutilus continued to besiege.