"Declare to me from the beginning, you Mousai who dwell in the house of Olympos, and tell me which of them first came to be.

In truth at first Khaos (Air) came to be, but next wide-bosomed Gaia (Earth), the ever-sure foundation of all the deathless ones who hold the peaks of snowy Olympos, and dim Tartaros (the Pit) in the depth of the wide-pathed Earth, and Eros (Love), fairest among the deathless gods, who unnerves the limbs and overcomes the mind and wise counsels of all gods and all men within them.

From Khaos (Air) came forth Erebos (Darkness) and black Nyx (Night); but of Nyx (Night) were born Aither (Light) and Hemera (Day), whom she conceived and bore from union in love with Erebos.

And Gaia (Earth) first bore starry Ouranos (Heaven), equal to herself, to cover her on every side, and to be an ever-sure abiding-place for the blessed gods. And she brought forth long Ourea (Mountains), graceful haunts of the goddess Nymphai who dwell amongst the glens of the hills. She bore also the fruitless deep with his raging swell, Pontos (Sea), without sweet union of love.

But afterwards she [Gaia, Earth] lay with Ouranos (Heaven) and bare deep-swirling Okeanos, Koios and Krios and Hyperion and Iapetos, Theia and Rhea, Themis and Mnemosyne and gold-crowned Phoibe and lovely Tethys. After them was born Kronos the wily." 

- Hesiod, Theogony 115

In the beginning there was 18. They were the Protogenoi; the first born of the immortals, who formed the very fabric of the universe.

There was Aether (Aither), the Protogenos of the mists of light which fill the upper zones of air; his element lay beneath the arch of heaven's dome, but high above the airs of the mortal realm. 

Ananke, the Protogeonos of inevitability, compulsion and necessity. 

Chaos (Khaos), the Protogenos of the lower air. She filled the gap between the bright mists of the heavenly aither and the floor of the earth. From Khaos were descended the other airs: Erebus (darkness), Nyx (night), Aether (light), Hemera (day); as well as the birds. A primeval mixture of the elements; the void by which everything was born.

Chronos (Khronos), the Protogenos of time.

Erebos (Erebus), the Protogenos of the mists of darkness; his dark element was sunk into the hollows of the earth, and encircled the dismal realm of the underworld.

Eros, the Protegonos of generation; he was one of the first beings to emerge at creation, and caused the universe to procreate.

Gaia (Gaea), the Protogenos of the Earth; Mother Earth emerged at the beginning of creation to form the foundation of the universe.

Hemera, the Protogenos of the day, rose up from the ends of the earth to scatter the dar