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

47. While this was going on at Veii, the Citadel of Rome and the Capitol were in very great danger. [2] For the Gauls had noticed the tracks of a man, where the messenger from Veii had got through, or perhaps had observed for themselves that the cliff near the shrine of Carmentis¹ afforded an easy ascent. So on a starlit night they first sent [p. 159]forward an unarmed man to try the way; [3] then² handing up their weapons when there was a steep place, and supporting themselves by their fellows or affording support in their turn, they pulled one another up, as the ground required, and reached- the summit, in such silence that not only the sentries but even the dogs —creatures easily troubled by noises in the night —were not aroused. [4] But they could not elude the vigilance of the geese, which, being sacred to Juno, had, notwithstanding the dearth of provisions, not been killed. This was the salvation of them all; for the geese with their gabbling and clapping of their wings woke Marcus Manlius, —consul of three years before and a distinguished soldier, —who, catching up his weapons and at the same time calling the rest to arms, strode past his bewildered comrades to a Gaul who had already got a foothold on the crest and dislodged him with a blow from the boss of his shield. [5] As he slipped and fell, he overturned those who were next to him, and the others in alarm let go their weapons and grasping the rocks to which they had been clinging, were slain by Manlius. [6] And by now the rest had come together and were assailing the invaders with javelins and stones, and presently the whole company lost their footing and were flung down headlong to destruction. [7] Then after the din was hushed, the rest of the night —so far as their excitement would permit, when even a past peril made them nervous —was given up to sleep. At dawn the trumpet summoned the soldiers to assemble before the tribunes. Good conduct and bad had both to be requited. [8] First Manlius was praised for his courage and presented with gifts, not only by [p. 161]the tribunes of the soldiers, but by agreement³ amongst the troops, who brought each half a pound of spelt and a gill of wine to his house, which stood in the Citadel. It is a little thing to tell, but the scarcity made it a great token of affection, since everyone robbed himself of his own sustenance and bestowed what he had subtracted from his physical necessities to do honour to one man. [9] Then the watchmen of the cliff which the enemy had scaled without being discovered were called up. [10] Quintus Sulpicius, the tribune, announced his intention to punish them all in the military fashion; but deterred by the cries of the soldiers, who united in throwing the blame upon a single sentinel, he spared the others. This man was guilty beyond a doubt, and was flung from the rock with the approval of all. [11] From that time the guards on both sides were more alert: the Gauls, because it had been put about that messengers were passing between Veii and Rome, the Romans, from their recollection of the peril of the night.