Titus Livius (Livy), The History of Rome, Book 5
D. Spillan, A.M., M.D., Ed.

43. The Gauls also, after having for several days waged an ineffectual war against the buildings of the city, when they saw that among the fires and ruins of the captured city nothing now remained except armed enemies, neither terrified by so many disasters, nor likely to turn their thoughts to a surrender, unless force were employed, determine to have recourse to extremities, and to make an attack on the citadel. [2] A signal being given at break of day, their entire multitude is marshalled in the forum; thence, after raising the shout and forming a testudo, they advance to the attack. [3] Against [p. 376]whom the Romans, acting neither rashly nor precipitately, having strengthened the guards at every approach, and opposing the main strength of their men in that quarter where they saw the battalions advancing, suffer the enemy to ascend, judging that the higher they ascended, the more easily would they be driven back down the steep. [4] About the middle of the ascent they met them: and making a charge thence from the higher ground, which of itself bore them against the enemy, they routed the Gauls with slaughter and destruction, so that never after, either [5??] in parties or with their whole force, did they try that kind of fighting. [6] Laying aside all hope of succeeding by force of arms, they prepare for a blockade; of which having had no idea up to [7??] that time, they had, whilst burning the city, destroyed whatever corn had been therein, and during those very days all the provisions had been carried off from the land to Veii. [8] Accordingly, dividing their army, they resolved that one part should plunder through the neighbouring states, that the other part should carry on the siege of the citadel, so that the ravagers of the country might supply the besiegers with corn.