Titus Livius (Livy), The History of Rome, Book 34
Evan T. Sage, Ph.D. Professor of Latin and Head of the Department of Classics in the University of Pittsburgh, Ed.

15. As his men grew weary, the consul rekindled their spirits by bringing up reserve cohorts from the second line. [2] A new line was established; fresh troops with unused weapons attacked the exhausted enemy and first, with a furious attack in wedge formation, pushed them back, then scattered them and put them to flight; with headlong speed they made across the fields for camp. [3] When Cato saw everything filled with confusion, he rode back to the second legion, which was in reserve, and ordered it to advance at quickened pace to attack the enemy's camp. [4] If a soldier in too great eagerness got ahead of the rank, he himself rode up between the lines and [p. 457]struck him with his spear-shaft, and ordered the tribunes¹ and centurions to punish him. By this time the camp was being attacked and the Romans driven back from the rampart with stones and poles and every sort of missile. [5] But when the new legion came up, the vigour of the attackers increased, and the enemy fought with greater desperation in defence of their rampart. [6] The consul scanned everything with his gaze, that he might break through wherever the resistance was weakest. He saw that there were few defenders at the left gate, and there he led the principes and hastati of the second legion. [7] The guard which was posted at the gate did not resist their onset; and the rest, seeing the enemy within the fortification, having lost their camp, likewise threw away their standards and arms. They were cut to pieces at the gates, where they were held fast in the narrow passages by their own numbers. [8] The soldiers of the second legion attacked them in the rear, the rest plundered the camp. [9] Valerius Antias relates that more than forty thousand of the enemy fell that day; Cato himself, a man not much inclined to be grudging in his own praise, says that many were killed, but does not give a definite number.