Titus Livius (Livy), The History of Rome, Book 4
Rev. Canon Roberts, Ed.

19. There was in the cavalry, on that day, a military tribune named A. Cornelius Cossus, a remarkably handsome man, and equally distinguished for strength and courage, and proud of his family name, which, illustrious as it was when he inherited it, was rendered still more so when he left it to his posterity. [2] When he saw the Roman squadrons shaken by the repeated charges of Tolumnius in whatever direction he rode, and recognised him as he galloped along the entire line, conspicuous in his royal habiliments, he exclaimed, ‘Is this the breaker of treaties between man and man, the violator of the law of nations? [3] If it is the will of heaven that anything holy should exist on earth, I will slay this man and offer him as a sacrifice to the manes of the murdered envoys.’ [4] Putting spurs to his horse he charged with levelled spear against this single foe, and having struck and unhorsed him, he leaped with the aid of his spear to the ground. [5] As the king was attempting to rise he pushed him back with the boss of his shield, and with repeated spear-thrusts pinned him to the earth. Then he despoiled the lifeless body, and cutting off his head stuck it on his spear, and carrying it in triumph routed the enemy, who were panic-struck at the king's death. So the enemy's cavalry, who had alone made the issue of the contest doubtful, now shared in the general rout. [6] The Dictator hotly pursued the flying legions and drove them to their camp with great slaughter. Most of the Fidenates, who were familiar with the country, escaped to the hills. Cossus with the cavalry crossed the Tiber and brought to the City an enormous amount of booty from the country of the Veientines. [7] During the battle there was also an engagement at the Roman camp with the detachment which, as already stated, Tolumnius had sent to attack it. [8] Fabius Vibulanus at first confined himself to the defence of the circuit of his lines; then, while the enemy's attention was wholly directed to forcing the stockade, he made a sortie from the Porta Principalis¹ on the right, and this unexpected attack produced such consternation among the enemy, that though there were fewer killed, owing to the smaller number engaged, the flight was just as disorderly as in the main battle.