Titus Livius (Livy), The History of Rome, Book 22
Benjamin Oliver Foster, Ph.D., Ed.

48. By this time the Roman left, where the cavalry of the allies had taken position facing the Numidians, was also engaged, though the fighting was at first but sluggish. It began with a Punic ruse. [2] About five hundred Numidians, who, in addition to their customary arms and missiles, carried swords concealed under their corslets, pretended to desert. [3] Riding over from their own side, with their bucklers at their backs, they suddenly dismounted and threw down bucklers and javelins at the feet of their enemies. Being received into the midst of their ranks they were conducted to the rear and ordered to fall in behind. [4] And while the battle was getting under way at every point, they kept quite still; but no sooner were the minds and eyes of all absorbed in the struggle, than they snatched up the shields which lay strewn about everywhere amongst the heaps of slain, and assailing the Romans from behind and striking at their backs and hamstrings, effected a great slaughter and a terror and confusion that were even greater. [5] And now in one place there was a panic rout and in another an obstinate though hopeless struggle,¹ when Hasdrubal, who commanded in that part of the field, withdrew the Numidians from the centre —since they fought but half-heartedly against men who met them face to face —and [6] dispatching them in pursuit of the scattered fugitives, sent in the Spanish and Gallic cavalry to help the [p. 359]Africans, who were now almost exhausted, though² more with slaying than with fighting.³