Titus Livius (Livy), The History of Rome, Book 27
Cyrus Evans, Ed.

49. More elephants were killed by their guides than by the enemy. They used to have with them a workman's knife, with a mallet. When these beasts began to grow furious, and attack their own party, the rider, placing this knife between the ears, just on the joint by which the neck is connected with the head, used to drive it in, striking it with all the force he could. [2] This was found to be the most expeditious mode of putting these bulky animals to death, when they had destroyed all hope of governing them. This method was first practised by Hasdrubal, a general whose conduct both frequently on other occasions, and especially in this battle, deserved to be recorded. [3] By encouraging the men when fighting, and sharing equally in every danger, he kept up the battle. Sometimes by entreating, at other times by rebuking, the troops, when tired and indisposed to fight from [p. 1158]weariness and over-exertion, he rekindled their spirits. [4] He called back the flying, and restored the battle in many places when it had been given up. At length, when fortune decidedly declared for the Romans, lest he should survive so great an army which had been collected under the influence of his name, he put spurs to his horse and rushed upon a Roman cohort, where he fell fighting, as was worthy of the son of Hamilcar and the brother of Hannibal. [5] At no time during that war were so many of the enemy slain in one battle; [6] so that a defeat equal to that sustained at Cannae, whether in respect of the loss of the general or the troops, was considered to have been retorted upon him. Fifty-six thousand of the enemy were slain, five thousand four hundred captured. [7] The other booty was great, both of every other kind, and also of gold and silver. In addition to the rest, there were recovered above four thousand Roman citizens, who had been taken by the enemy, which formed some consolation for the soldiers lost in that battle. For the victory was by no means bloodless. [8] Much about eight thousand of the Romans and the allies were slain; and so completely were even the victors satiated with blood and slaughter, that the next day, when Livius the consul received intelligence that the Cisalpine Gauls and Ligurians, who had either not been present at the battle or had made their escape from the carnage, were marching off in one body without a certain leader, without standards, without any discipline or subordination; [9] that if one squadron of horse were sent against them they might be all destroyed, he replied, “Let some survive to bear the news of the enemy's losses and of our valour.”