From Appian's History of Rome: The Spanish Wars
[§44] [154] Some years later another serious war broke out in Spain for the following reason: Segeda, a large and powerful city of a Celtiberian tribe called the Belli, was included in the treaties made by Gracchus. It persuaded some of the smaller towns to settle in its own borders, and then surrounded itself with a wall seven kilometers in circumference. It also forced the Titthi, a neighboring tribe, to join in the undertaking.
When the Senate learned this, it forbade the building of the wall, demanded the tribute imposed by Gracchus, and ordered the inhabitants to furnish a contingent for the Roman army, for this was one of the stipulations of the treaty made with Gracchus. As to the wall the Celtiberians replied that they were forbidden by Gracchus to build new cities, but not forbidden to fortify existing ones. As to the tribute and the military contingent they said that they had been released from these requirements by the Romans themselves subsequently. This was true, but the Senate, when granting these exemptions, always added that they should continue only during the pleasure of the Roman people.
[§45] [153] Accordingly the praetor [Quintus Fulvius] Nobilior was sent against them with an army of nearly 30,000 men. When the Segedians learned of his coming, their wall not being yet finished, they fled with their wives and children to the Arevaci and begged that the latter would receive them. The Arevaci did so, and also chose a Segedian named Carus, whom they considered skillful in war, as their general. On the third day after his election he placed 20,000 foot and 500 horse in ambush in a dense forest and fell upon the Romans as they were passing through. The battle was for a long time doubtful, but in the end he gained a splendid victory, 6,000 Roman citizens being slain. So great a disaster befell the city on that day.
But while he was engaged in a disorderly pursuit after the victory, the Roman horsemen, who were guarding the baggage, fell upon him and killed Carus himself, who was performing prodigies of valor, and not less than 6,000 others with him. Finally night put an end to the conflict. This disaster happened on the day on which the Romans are accustomed to celebrate the festival of Vulcan [23 August 153]. For which reason, from that time on, no general will begin a battle on that day unless compelled to do so.
 
[§46] [153] The Arevaci convened immediately, even in the night, at Numantia, which was a very strong city, and chose Ambo and Leuco as their generals. Three days later [the praetor Quintus Fulvius] Nobilior advanced and pitched his camp at some four kilometers from the place.
Here he was joined by 300 horse and ten elephants sent to him by Massinissa. When he moved against the enemy he placed these animals in the rear where they could not be seen. Then when battle was joined the army divided and brought the elephants into view. The Celtiberians and their horses, who had never seen elephants before, were thunderstruck and fled to the city.
Nobilior advanced at once against the city walls, where the battle raged fiercely, until one of the elephants was struck on the head with a large falling stone, when he became savage, uttered a loud cry, turned upon his friends, and began to destroy everything that came in his way, making no distinction between friend and foe. The other elephants, excited by his cries, all began to do the same, trampling the Romans under foot, scattering and hurling them this way and that. (This is always the way with elephants when they are enraged. Then they take everybody for foes; wherefore some people call them the common enemy, on account of their fickleness.)
The Romans took to disorderly flight. When the Numantines perceived this they sallied out and pursued them, killing about 4,000 men and three elephants. They also captured many arms and standards. The loss of the Celtiberians was about 2,000.
[§47] Nobilior, recovering a little from this disaster, made an attack upon the stores which the enemy had collected at the town of Axinium, but he accomplished nothing, and having lost many of his men there, he returned by night to his camp. Thence he sent Biesius, his master of horse, to secure the alliance of a neighboring tribe and to ask for assistance in the way of cavalry. They gave him some, and as he was returning with them the Celtiberians laid an ambush for him. The ambush was discovered and the allies escaped, but Biesius, who engaged the enemy, was killed and many of his soldiers with him.
Under the influence of such a succession of disasters to the Romans, the town of Ocilis, where their provisions and money were stored, revolted to the Celtiberians. Then Nobilior in despair went into winter quarters in his camp, sheltering himself as well as he could. He suffered much from scantiness of supplies, having only what was inside the camp, and from heavy snowstorms and severe frost, so that many of his men perished while outside gathering wood, and others inside fell victims to confinement and cold.
