In Greek mythology , Ophion ("serpent"), also called Ophioneus ruled the world with Eurynome before the two of them were cast down by Cronus and Rhea, according to some sources. Pherecydes of Syros's Heptamychia is the first attested mention of Ophion.

The story was apparently popular in Orphic poetry, of which only fragments survive.

Apollonius of Rhodes in his Argonautica (1.495f) summarizes a song of Orpheus:

He sang how the earth, the heaven and the sea, once mingled together in one form, after deadly strife were separated each from other; and how the stars and the moon and the paths of the sun ever keep their fixed place in the sky; and how the mountains rose, and how the resounding rivers with their nymphs came into being and all creeping things. And he sang how first of all Ophion and Eurynome, daughter of Oceanus, held the sway of snowy Olympus, and how through strength of arm one yielded his prerogative to Cronos and the other to Rhea, and how they fell into the waves of Oceanus; but the other two meanwhile ruled over the blessed Titan-gods, while Zeus, still a child and with the thoughts of a child, dwelt in the Dictaean cave; and the earthborn Cyclopes had not yet armed him with the bolt, with thunder and lightning; for these things give renown to Zeus.

Lycophron (1191) relates that Zeus' mother, that is Rhea, is skilled in wrestling, having cast the former queen Eurynome into Tartarus.

Nonnus in his Dionysiaca has Hera say (8.158f):

I will go to the uttermost bouds of Oceanus and share the hearth of primeval Tethys; thence I will pass to the house of Harmonia and abide with Ophion.

Harmonia here is probably an error in the text for Eurynome. Ophion is mentioned again by Nonnus (12.43):

Beside the oracular wall she saw the first tablet, old as the infinite past, containing all the things in one: upon it was all that Ophion lord paramount had done, all that ancient Cronus accomplished.

We also have fragments of the writings of the early philosopher Pherecydes of Syros (6th century BC) who devised a myth or legend in which powers known as Zas and Chronos 'Time' and Chthonie 'Of the Earth' existed from the beginning and in which Chronos creates the universe. Some fragments of this work mention a birth of Ophioneus and a battle of the gods between Cronus (not Chronos) on one side and Ophioneus and his children on the other in which an agreement is made that however pushes the other side into Ogenos will lose and the winner will hold heaven.

Eusebius of Caearea in his Praeparatio (1.10) cites Philo of Byblos as declaring that Pherecydes took Ophion and the Ophionidae from the Phoenicians.

Robert Graves in his book The Greek Myths (ISBN 0140171991) attempted to reconstruct a supposed Pelasgian creation myth involving Ophion as a serpent created by a supreme goddess called Eurynome dancing on the waves. She is fertlized by the serpent and in the form of Night lays a golden egg on the waters about which Ophion entwines until eventually it hatches and the world issues forth. Then Ophion and Eurynome dwell in the world on Mt. Olympus until Ophion's boasting leads Eurynome to banish him to the darkness below the earth.

Most have found it poetic but too freely and obviously constructed to fit Grave's theories to be convincing, too different from the texts that we have and too idiosyncratic.

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Ophion is also a genus of family Ichneumonidae (parasitic wasps)

The Greek Myths: The Complete And Definitive Edition, Robert Graves

Greek Mythology