Areion, also called Arion, is an immortal horse conceived by Demeter, the goddess of agriculture and harvest, and Poseidon, the ocean god, while they were both in the form of horses.
In most stories, Areion was conceived while the goddess Demeter hid from her brother Poseidon under the guise of a mare. Aerion was a result of Poseidon seeing through the ruse. Other sources say that Areion's mother was Gaia, the goddess of the earth itself. Others claim Areion was sired by Zephyrus, one of the four wind-gods, and that its mother was a Harpy.
Areion was extremely swift and had the power of speech. He was once owned by Heracles (better known as Hercules). It was also owned by Oncius of Arcadia and Adrastus, King of Argos.
Heracles stole Areion from Oncius, then rode it in battle against the Eleans. After the war, he gave the immortal horse to Adrastus.
Areion is mentioned by the ancient poets Homer and Sextus Propertius, and the geographer Pausanias.