 There were hollows and dead patches of land in the ground behind and beside the hill where soldiers could hide without being noticed.Hannibal selected a picked body of 5,000 infantry and 500 cavalry, and ordered them to conceal themselves in groups of 200-300 in the hollows and dead ground on the night before the battle.The skill and discipline of the Carthaginians is evident through their flawless execution of this potentially hazardous operation.