Demetrius was received warmly by the young king whose father was also called Demetrius, becoming one of Philip's most trusted advisors. According to Polybius, Demetrius was instrumental in turning Philip's ambitions toward Illyria and Rome. In 217 BC when Philip learned of the victory of Hannibal, the Carthaginian general, over the Romans, at Lake Trasimene, Philip at first showed the letter only to Demetrius. Perhaps seeing a chance to recover his possessions in Illyria and exact a measure of revenge on Rome, Demetrius immediately advised the young king to make peace with the Aetolians, with whom Philip was at war, and turn his attentions westward. In summarising the strategy needed for the situation, Polybius states that Demetrius said: