Numidian cavalry lured Sempronius out of his camp and onto ground of Hannibal's choosing, where the Battle of the Trebia took place. Fresh Carthaginian cavalry routed the outnumbered Roman cavalry, and Carthaginian light infantry outflanked the Roman infantry. A previously hidden Carthaginian force attacked the Roman infantry in the rear. Most of the Roman units then collapsed and most Romans were killed or captured by the Carthaginians, but 10,000 under Sempronius maintained formation and fought their way out to the safety of Placentia. Recognising the Carthaginians as the dominant force in Cisalpine Gaul, Gallic recruits flocked to them and their army grew to 60,000.