Homer illustrated Paeon the god, and the song both of apotropaic thanksgiving or triumph.[citation needed] Such songs were originally addressed to Apollo, and afterwards to other gods: to Dionysus, to Apollo Helios, to Apollo's son Asclepius the healer. About the 4th century BCE, the paean became merely a formula of adulation; its object was either to implore protection against disease and misfortune, or to offer thanks after such protection had been rendered. It was in this way that Apollo had become recognised as the god of music. Apollo's role as the slayer of the Python led to his association with battle and victory; hence it became the Roman custom for a paean to be sung by an army on the march and before entering into battle, when a fleet left the harbour, and also after a victory had been won.