Titus Livius (Livy), The History of Rome, Book 26
Frank Gardner Moore, Professor Emeritus in Columbia University, Ed.

17. at Rome the senate, having discharged its responsibilities so far as concerned Capua, voted to assign to Gaius Nero six thousand infantry and three hundred cavalry of his own choosing, from the two legions which he had had before Capua, and from the Latin allies the same number of infantry and eight hundred cavalry. this army Nero embarked at Puteoli and transported to Spain. [2] arrived at Tarraco by sea, he there disembarked his troops, beached the ships, and armed even the crews, to increase his numbers. then setting out for the river Ebro, he took over the army from Tiberius Fonteius and Lucius Marcius.¹ [3] he thereupon proceeded against the enemy. Hasdrubal, the son of Hamilcar, was encamped at the Black Rocks. the place is in the country of the Ausetani,² between the towns of Iliturgis³ and Mentissa. [4] Nero occupied the entrance to this pass. Hasdrubal, to avoid being entrapped, sent a herald to promise that if he should be allowed to get away, he would transport his entire army out of Spain. [5] the Roman accepted the proposal with joy, and Hasdrubal asked for the next day for a conference, that in person [6??] they might draw up [p. 67]the terms for the surrender of the citadels of cities⁴ and fix a date before which the garrisons were to be evacuated, and the Carthaginians might remove all their property without molestation. [7] having gained that request, Hasdrubal at once gave orders that at dusk and then all through the night the heaviest troops should escape from the pass by any possible way. [8] Great pains were taken not to have many leave that night, that even their small numbers might be better suited both to escaping the enemy's notice by silence and to making their way out by narrow and difficult paths. [9] next day they came to the conference;⁵ but by speaking at unnecessary length and by purposely writing what was not to the point the day was spent, and postponement taken to the next day. the addition of the following night gave them time to send out others as well; [10] and on the following day the business did not reach an end. [11] Thus several days were spent in arguing openly about terms, and several nights in secretly sending Carthaginians away from the camp. and after the larger part of the army had been sent away, they ceased any longer to stand by even what they had been the first to propose. and there was less and less agreement, as honesty declined along with fear. [12] by this time nearly all the infantry forces had escaped from the pass when at daybreak a dense fog covered the whole pass and the adjacent plain. Hasdrubal on noticing that, sent a messenger to Nero, to postpone the conference until the next day: that day was banned among the Carthaginians, he said, for the doing of anything serious. [13] as even then fraud was [p. 69]not suspected, excuse for that day was granted, and⁶ forthwith Hasdrubal with his cavalry and elephants left camp, and without any noise escaped to a place of safety. at about the fourth hour the burning away of the fog by the sun cleared the air, and the Romans caught sight of the empty camp of the enemy. [14] when Claudius, who until then did not recognize the Punic deception, perceived that he had been tricked, he pressed the pursuit of a departing enemy, [15??] he being all ready to engage in pitched battle. [16] but the enemy refused to fight. and yet there were slight engagements between the rear of the Carthaginian column and the advance guard of the Romans.