I think this pairing has been unfairly overlooked in the Riordanverse. Because a god in Greek mythology and a goddess in Roman mythology sounds like an extremely awkward situation for a group of Greco-Roman demigods. And the fact that Eternitas had some influence in Rome (she was printed on coins) seems like a completely missed opportunity.
Aeternitas is a Roman goddess personifying eternity and immortality, often depicted on coins as a woman with attributes of continuity: an ouroboros (a snake biting its tail), a phoenix, the globe, celestial bodies (sun, moon), an elephant, or a scepter. She symbolized the eternal power of the empire and the afterlife.
Aion (Aion, Ancient Greek: Αἰών "lifetime", "generation") is a deity in ancient Greek mythology and theocosmogony[2], the personification of the entire duration of time (sometimes translated as "eternity"). Presumably associated with Iranian ideas about Zurvan. In Roman mythology, Aion corresponds to Aeternitas.
Aeon is mentioned in the Orphic Hymn to Musaeus. According to a disputed fragment of Epimenides, this is the name of one of the Dioscuri (Dioscuri (Ancient Greek: Διόσκουροι - "sons of Zeus") - in ancient mythology, the twin brothers Castor and Polydeuces (Pollux), children of Leda. They were considered the patrons of travelers, sailors, gymnastics, and a symbol of brotherly love. The constellation Gemini, where Zeus placed the brothers after their death, is named in their honor), with the second Dioscuri being a woman, Physis. It is identified with the penis of Cronus. (lol) The image is found in Heraclitus, who calls it "a child playing on a throne." It is mentioned repeatedly by Nonnus.
