Titus Livius (Livy), The History of Rome, Book 5
Benjamin Oliver Foster, Ph.D., Ed.

38. There the tribunes of the soldiers, without having selected a place for a camp or fortified a position to which they might retreat, and, forgetting even the gods, to say nothing of men, without auspices or sacrificial omens, drew up their line with the wings extended to prevent being outflanked by the numbers of the enemy; yet could not stretch their front as wide as his, though they thinned it till the centre was weak and scarce held together. [2] There was a little eminence on the right which they decided to occupy with their reserves, a measure which, though it was the beginning of their panic and flight, was also the sole salvation of the fugitives. [3] For Brennus, the Gallic chieftain, seeing the Romans to be so few, was especially apprehensive of a stratagem. He supposed that they had seized the higher ground' for this purpose, that when the Gauls had made a frontal attack on the battle-line of the legions, the reserves might assail them in the flank and rear. [4] He therefore directed his assault against the reserves, not doubting that, if he could [p. 131]dislodge them, it would be easy for his greatly¹ superior numbers to obtain a victory in the plain. Thus not only luck but generalship as well were on the side of the barbarians. [5] In the other army there was no resemblance to Romans, either amongst officers or private soldiers. Terror and dismay had got hold of their spirits, and such complete forgetfulness of everything that a much greater number fled to Veii, a hostile city, though the Tiber was across their way, than by the straight road to Rome, to their wives and children. For a little while the reserves were protected by their position. [6] In the rest of the field, no sooner had those who were nearest heard the shouting on their flank, and those who were farthest the outcry in their rear, than — fresh and unhurt —they ran away from their strange enemies, almost before they had caught sight of them; and so far were they from risking a combat, that they did not even return their battle-cry. [7] None were slain in fight; but they were cut down from behind as they blocked their escape by their own struggles in the disordered rout. [8] On the bank of the Tiber, whither the whole left wing had fled, after throwing away their arms, there was great slaughter, and many who could not swim, or lacked the strength, weighed down by their corslets and other armour, sank beneath the flood. [9] Nevertheless, the chief part got safely to Veii, whence they not only sent no succours to Rome, but dispatched not even a messenger to tell of the defeat. [10] From the right wing, which had stood at a distance from the river and closer to the foot of the mountain, the fugitives all made for Rome, and without stopping even to shut the city gates, sought refuge in the Citadel.

[p. 133]