Titus Livius (Livy), The History of Rome, Book 27
Frank Gardner Moore, Professor Emeritus in Columbia University, Ed.

2. Marcellus, who was not particularly alarmed by so serious a defeat, wrote a letter to the senate at Rome in regard to the loss of general and army at Herdonea. [2] He said that nevertheless, being the same man who, after the battle of Cannae, had frustrated Hannibal, elated by that victory, he was marching against him to cut short his joy and exultation. [3] At Rome, to be sure, there was not only great sorrow owing to what had happened, but also great fear for the future. [4] The consul, however, crossing over from Samnium into Lucania, pitched camp near Numistro,¹ on level ground in sight of Hannibal, while the Carthaginian held a hill. [5] He added the further appearance of confidence in being the first to lead out into battle-line. And Hannibal did not refuse, when he saw the standards borne out of the gates. Nevertheless they drew up their lines so that the Carthaginian made his right wing reach up the hill, while the Romans rested their left wing on the town. [6] [p. 209]On the Roman side the first legion and right ala, on² Hannibal's side the Spanish soldiers and Balearic slingers were engaged; and the elephants also were driven into battle after the conflict had begun. [7] For a long time the battle hung in the balance, not inclining in either direction. After they had prolonged the battle from the third hour to nightfall and the front lines were exhausted by fighting, the third legion relieved the first, the left ala relieved the right, and among the enemy fresh troops took over the battle from the weary. [8] A new battle and fierce suddenly flamed out of a conflict now grown spiritless, for the combatants were now fresh in spirit and in body. [9] But night parted them with victory undecided. On the next day the Romans stood in line from sunrise until late in the day. When none of the enemy came out against them, they gathered spoils at their leisure, carried corpses of their men into one place and burned them. [10] On the following night Hannibal broke camp silently and marched away into Apulia. Marcellus, when day disclosed the flight of the enemy, left the wounded at Numistro with a small garrison, placed Lucius Furius Purpurio, a tribune of the soldiers, in command of them, and made haste to follow on Hannibal's heels. [11] Near Venusia³ he overtook him. There for a number of days, while charges were made by outposts, there were mixed cavalry and infantry engagements, rather skirmishes than important battles, and nearly all of them favourable to the Romans. [12] Thence the armies were led through Apulia without any notable conflict, since Hannibal [p. 211]would set his standards in motion by night, seeking⁴ positions for ambuscades, while Marcellus did not follow except in broad daylight and after reconnoitring.