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

14. When this was reported to Hannibal, “Of a truth,” he said, “we have to deal with an enemy who can bear neither good fortune nor bad. If he has won, he furiously presses the defeated; if on the other hand he has been defeated, he renews the conflict with the victors.”¹ [2] Then he ordered the trumpets to sound and led out his forces. On both sides the battle was much fiercer than the day before, the Carthaginians striving to maintain the distinction of yesterday, while the Romans strove to rid themselves of their disgrace. [3] The left ala on the Roman side and the cohorts which had lost their standards were fighting in the first line, and the eighteenth legion was drawn up on the right wing. [4] Lucius Cornelius Lentulus and Gaius Claudius Nero, the lieutenants, commanded the wings. Marcellus in person upheld the centre, to exhort them and as a witness. On Hannibals' side Spanish troops held the front line. [5] And they were the best troops in the entire army. [6] When the battle had long been indecisive Hannibal ordered the elephants to be driven up to the front, in the hope that that move might [p. 265]bring about confusion and panic. [7] And at first they² did cause disorder among the standards and ranks, and by trampling down some of those who were near, and scattering others in alarm, they had stripped the line of battle at one point, and the flight would [8??] have spread further, had not Gaius Decimius Flavus, a tribune of the soldiers, seized a standard from the first maniple of the hastati³ and ordered the maniple to which it belonged to follow him. He led them to the spot where the brutes massed together were causing confusion and bade them hurl their javelins against them. [9] All the weapons stuck fast, for it was not difficult to hit bodies of such size from a short distance and now packed in a dense mass. But although not all were wounded, still those in whose backs the javelins remained well fixed —so undependable is the species —took to flight and even made the uninjured wheel about. [10] Then no longer did a single maniple hurl its javelins, but every soldier for himself, provided he was able to catch up with the column of the fleeing elephants. All the more did the brutes dash among their own men and cause a greater slaughter than they had done among the enemy, in proportion as the frightened beast is urged on more fiercely by terror than when under the control of a driver on its back. [11] Into the line thrown into confusion by the brutes dashing through it the Roman infantry carried their standards and with no great struggle they made the scattered and wavering enemy retreat. [12] Then, as they fled, Marcellus sent his cavalry against them, and pursuit did not end until in alarm they were driven into their camp. [13] For in addition to the other causes of terror and consternation, two elephants had fallen in the very gate, [p. 267]and the soldiers were forced to dash into the camp⁴ over fosse and earthwork. It was there that the greatest slaughter of the enemy occurred, that is to say, about eight thousand men and five elephants. [14] And for the Romans also it was not a bloodless victory. About one thousand seven hundred from the two legions, and of the allies more than one thousand three hundred, were killed; wounded were a large number of citizens and allies. [15] Hannibal moved his camp that night; Marcellus was eager to pursue, but the numbers of the wounded prevented him.