Arion

Arion is an immortal horse in Greek mythology. Arion's parents were Demeter and Poseidon. Demeter had taken the form of a mare in order to escape Poseidon, by hiding among a pack of other horses. However, he saw through her guise and turned himself into a stallion, mating with her. Arion and his sister Despoina were born from their union. Arion was extremely swift and endowed with speech.

Books

 * Arion appears in The Son of Neptune, a novel by Rick Riordan, sequel to The Lost Hero. He reappears in the third installment of the series, The Mark of Athena, as well as in The House of Hades . He also makes an appearance in The Blood of Olympus.