Carthage seems to have fielded a formidable cavalry force, especially in its Northwest African homeland; a significant part of it was composed of light Numidian cavalry, who were considered "by far the best horsemen in Africa". Their speed and agility proved pivotal to several Carthaginian victories, most notably the Battle of Trebia, the first major action in the Second Punic War. The reputation and effectiveness of Numidian cavalry was such that the Romans utilized a contingent of their own in the decisive Battle of Zama, where they reportedly "turned the scales" in Rome's favor. Polybius suggests that cavalry remained the force in which Carthaginian citizens were most represented following the shift to mostly foreign troops after the third century BC.