Following these events, Carthage sued for peace, but the terms demanded by Regulus were too harsh, and the war continued. The Carthaginians began to quickly expand their military capabilities on land, conscripting their own citizens and recruiting more mercenaries, including Spartan captain Xanthippus, who was charged with retraining and restructuring the Carthaginian army. Xanthippus adopted the combined arms model of the Macedonian army, developed during the time of Phillip II. Xanthippus split his cavalry between his two wings, with mercenary infantry screening the cavalry, and a hastily raised citizen phalanx in the center screened by a line of elephants in front of the spearmen. Previously, Carthaginian generals had placed the elephants behind the central phalanx. Xanthippus also realized the mistakes that the Carthaginians were making by avoiding open ground battles against the Romans, instead seeking only uneven terrain. This was done out of fear of the Romans' superior infantry. Such a strategy, however, restricted Carthage's strongest elements: its cavalry and elephants. Uneven terrain also disrupts the phalanx in favor of the more flexible legion. By seeking battles on open plains, Xanthippus was able to make the fullest use of Carthage's strengths, where Roman formations broke under attack from the elephant and cavalry charges.