Hannibal had deployed his forces based on the particular fighting qualities of each unit, taking into consideration both their strengths and weaknesses. This aspect of Hannibal's leadership was highlighted in the use of a Spanish unit, the Balearic slingers, whom he placed behind the infantry to hurl their ranged missiles into the masses of Roman troops. He placed his Iberians or Celtiberians and Gauls in the middle, alternating the ethnic composition between Spaniards and Gauls across the front line, with himself at the front and center alongside his brother Mago. Roman sources claim their placement was chosen for being the most expendable and unreliable troops, but modern reflections believe those forces were actually selected for their battle-hardening to carry the weight of the Punic side, as they were tasked with the controlled retreat that ultimately made possible Hannibal's pincer movement. Meanwhile, infantry from Punic Africa was on the wings at the very edge of his infantry line. This infantry would remain cohesive and attack the Roman flanks.