Titus Livius (Livy), The History of Rome, Book 25
Frank Gardener Moore, Professor Emeritus in Columbia University, Ed.

32. In Spain in the same summer, when for about two years¹ nothing very notable had occurred and the war was being waged more by diplomacy than by arms, the Roman generals, on leaving their winter-quarters, united their forces. [2] Thereupon a council was called and all were of one mind, that, since up to that time they had accomplished nothing except to hold Hasdrubal back from pushing on into Italy, it was time that their task should now be to end the war in Spain. [3] And they believed they had sufficient reinforcements for that purpose in twenty thousand Celtiberians who had been called to arms that winter. [4] The enemy had three armies. Hasdrubal, the son of Gisgo, and Mago with adjoining camps were about five days' march from the Romans. [5] Nearer was Hasdrubal, the son of Hamilcar, a veteran commander in Spain. He had his army near a city called Amtorgis. [6] It was he that the [p. 465]Roman generals wished first to overpower; and they² hoped they had quite ample forces for that end. The one remaining concern was the fear that, if he was defeated, the other Hasdrubal and Mago might in alarm withdraw to pathless forests and mountains and prolong the war. [7] They thought it best therefore to divide their forces into two armies and include the whole of Spain in their plan of operations. And they divided in such manner that Publius Cornelius should lead two-thirds of the army of Romans and allies against Mago and Hasdrubal, and [8??] that Gnaeus Cornelius with one-third of the old army and the Celtiberians in addition should carry on the war with Hasdrubal Barca. [9] Setting out together, with the Celtiberians in the van, both generals and armies pitched camp near the city of Amtorgis, in sight of the enemy, but separated by a river.³ [10] There Gnaeus Scipio remained with the above-mentioned forces, while Publius Scipio set out for his previously appointed share of the war.