On this occasion we see Scipio employing two different stratagems.
Observing that Hasdrubal always brought ship troops out of camp at a late hour and drew them up with the Libyans in the centre and the elephants in front of the two wings, and having himself been in the habit of delaying until a later hour
and of opposing the Romans to the Libyans in the centre and stationing the Spaniards on his wings, he acted on the day on which he had decided to deliver the decisive battle in a precisely opposite manner, and thus much contributed to the victory of his own army and the discomfiture of the enemy.
For as soon as it was light he sent a message by his aides-de-camp to all the tribunes and soldiers to take their morning meal and arm themselves and march out of the camp.
When this was done, all showing great zeal in carrying out the order, as they suspected what was in the wind, he sent on the cavalry and light infantry with orders to get close up to the enemy's camp and shoot at him boldly, while he himself with his infantry advanced just as the sun was rising, and when he reached the middle of the plain, formed in order of battle, disposing his troops in an order contrary to that which he had previously used, as he placed the Spaniards in the centre and the Romans on the wings.
The Carthaginians, upon the enemy's cavalry coming suddenly up to their camp and the rest of his army forming up in full view, scarcely had time to arm themselves.
So that Hasdrubal, with his men still fasting, was obliged on the spur of the moment and without any preparation to send off his own cavalry and light infantry to engage those of the enemy on the plain and to draw up his heavy infantry on the level ground at no great distance from the foot of the hill, as was his usual practice.
For a certain time the Romans remained inactive, but when, as the day advanced, there was no decisive advantage on either side in the engagement of the light-armed troops, those who were hard pressed always retreating to the shelter of their respective phalanxes and then issuing forth again to resume the combat,
Scipio receiving the skirmishers through the intervals between his cohorts distributed them on his wings behind his infantry, placing the velites in front with the horse behind them. At first he made a direct frontal advance,
but when at a distance of four stades from the enemy he ordered the Spaniards to continue advantage in the same order but the infantry and cavalry on the right wing to wheel to the right and those of the left wing to wheel to the left.
Walbank Commentary