L'Art d'aimer
The romantic nature of their relationship was first described by Callimachus of Alexandria, who wrote that Apollo was "fired with love" for Admetus. Plutarch lists Admetus as one of Apollo's lovers and says that Apollo served Admetus because he doted upon him. Latin poet Ovid in his Ars Amatoria said that even though he was a god, Apollo forsook his pride and stayed in as a servant for the sake of Admetus. Tibullus describes Apollo's love to the king as "servitium amoris" (slavery of love) and asserts that Apollo became his servant not by force but by choice.