Eternium was a close confidant of Kastalia, and inhabited her temple. He was a manifestation of the River of Eternity, which was sacred to the Goddess.
In summer of 584 the Order of the River cared for Etermnium after he suffered a mysterious ailment. Beneath the prominence of the Tear constellation they ritually restored the spirit's vitality, awakening Ourania's daughter and bringing the Fluvial Queen's attention back to Achaea.