Titus Livius (Livy), The History of Rome, Book 28
Cyrus Evans, Ed.

1. AT the time when Spain appeared to be relieved in proportion to the degree in which the weight of the war was removed into Italy, by the passage of Hasdrubal, another war sprang up there equal in magnitude to the former. [2] At this juncture, the Romans and Carthaginians thus occupied Spain: Hasdrubal, son of Gisgo, had retired quite to the ocean and Gades; [3] the coast of our sea, and almost the whole of that part of Spain which lies eastward, was subject to Scipio and the Romans. [4] The new general, Hanno, who had passed over from Africa, to supply the place of the Barcine Hasdrubal, with a new army, and formed a junction with Mago, having in a short time armed a large number of men in Celtiberia, which lies in the midway between [5??] the two seas, Scipio sent Marcus Silanus against him, with no more than ten thousand infantry and five hundred horse. [6] Silanus, by marching with all the haste he could, (though the ruggedness of the roads, and narrow defiles obstructed with thick woods, which are [p. 1162]very frequent in Spain, impeded him,) yet being guided by deserters from Celtiberia, natives of that place, reached the enemy, anticipating not only messengers but even all rumour of his coming. [7] From the same source he ascertained, when they were about ten thousand paces from the enemy, that they had two camps, one on each side of the road in which they were marching; that the Celtiberians, a newly-raised army, in number above nine thousand, were on the left, and that the Carthaginian camp was stationed on the right. [8] The latter was secured and protected by outposts, watches, and every kind of regular military guard, while the former was disorderly and neglected, as belonging to barbarians, who were raw soldiers, and were under the less apprehension, because they were in their own country. [9] Silanus, concluding that this was the camp to be attacked first, ordered the troops to march as much as possible towards the left, lest he should be observed from any point by the Carthaginian outposts, and sending scouts in advance, pushed on towards the enemy at a rapid pace.