Titus Livius (Livy), The History of Rome, Book 10
Benjamin Oliver Foster, Ph.D., Ed.

27. The consuls came up with the enemy —who had crossed the Apennines —in the territory round Sentinum, and went into camp about four miles off. [2] consultations were then held amongst the enemy and they decided not to unite all their forces in one camp nor to give battle all together; to the Samnites were joined the Gauls and to the Etruscans the men of Umbria. [3] a day was designated for the battle, and the Samnites and Gauls were appointed to make the attack; in the midst of the engagement the Etruscans and the Umbrians were to assault the Roman camp. [4] These plans were upset by three Clusinian deserters who came over secretly in the night to Fabius, and having informed him of the enemy's designs were rewarded and sent back again, so that from time to time, as each new [p. 463]step should be decided on, they might find it out¹ and report upon it. [5] The consuls wrote to Fulvius and Postumius to march from their respective posts in the Faliscan and Vatican districts to Clusium, and lay waste the territories of the enemy with the utmost rigour. [6] The reports of this devastation drew off the Etruscans from the region of Sentinum to the defence of their own frontiers. [7] thereupon the consuls strove to bring about an engagement in their absence. for the space of two days they harassed the enemy, but in these two days there was nothing done worth telling: a few were slain on either side and spirits were whetted for a downright battle, but the main issue was not brought to a decision. [8] on the third day the opposing armies descended in full strength into the field.

as they stood arrayed for battle, a hind, pursued by a wolf that had chased it down from the mountains, fled across the plain and ran between the two lines. they then turned in opposite directions, the hind towards the Gauls, the wolf towards the Romans. for the wolf a passage was opened between the ranks, but the hind was killed by the Gauls. [9] then one of the front —rankers on the Roman side called out, “that way flight and slaughter have shaped their course, where you see the beast lie slain that is sacred to Diana; on this side the wolf of Mars, unhurt and sound, has reminded us of the Martian race and of our Founder.”²

[10] on the right wing stood the Gauls, on the left the Samnites. facing the Samnites, Quintus Fabius drew up the first and third legions, to form the Roman right, while Decius marshalled the fifth and sixth on the Roman left, against the Gauls. [11] The [p. 465]second and the fourth were campaigning in Samnium³ under Lucius Volumnius the proconsul. at the first shock the strength put forth on both sides was so equal that if the Etruscans and the Umbrians had been present either in the battle or at the camp, in whichever quarter they had thrown their weight the Romans must have suffered a disaster.