And there, all in their order, are the sources and ends of gloomy earth and misty Tartarus and the unfruitful sea and starry heaven, loathsome and dank, which even the gods abhor.

It is a great gulf, and if once a man were within the gates, he would not reach the floor until a whole year had reached its end, but cruel blast upon blast would carry him this way and that. And this marvel is awful even to the deathless gods.

There stands the awful home of murky Night wrapped in dark clouds. In front of it the son of Iapetus [Atlas] stands immovably upholding the wide heaven upon his head and unwearying hands, where Night and Day draw near and greet one another as they pass the great threshold of bronze: and while the one is about to go down into the house, the other comes out at the door.

And the house never holds them both within; but always one is without the house passing over the earth, while the other stays at home and waits until the time for her journeying come; and the one holds all-seeing light for them on earth, but the other holds in her arms Sleep, the brother of Death, even evil Night, wrapped in a vaporous cloud.

And there the children of dark Night have their dwellings, Sleep and Death, awful gods. The glowing Sun never looks upon them with his beams, neither as he goes up into heaven, nor as he comes down from heaven. And the former of them roams peacefully over the earth and the sea’s broad back and is kindly to men; but the other has a heart of iron, and his spirit within him is pitiless as bronze: whomsoever of men he has once seized he holds fast: and he is hateful even to the deathless gods.
(Hesiod, Theogony, 715ff)

So they, with bitter wrath, were fighting continually with one another at that time for ten full years, and the hard strife had no close or end for either side, and the issue of the war hung evenly balanced. But when he had provided those three [Briareus and Cottus and Gyes] with all things fitting, nectar and ambrosia which the gods themselves eat, and when their proud spirit revived within them all after they had fed on nectar and delicious ambrosia, then it was that the father of men and gods [Zeus] spoke amongst them: ‘Hear me, bright children of Earth and Heaven, that I may say what my heart within me bids. A long while now have we, who are sprung from Cronos, and the Titan gods fought with each other every day to get victory and to prevail. But do you show your great might and unconquerable strength, and face the Titans in bitter strife; for remember our friendly kindness, and from what sufferings you are come back to the light from your cruel bondage under misty gloom through our counsels.’

So he said. And blameless Cottus answered him again: `Divine one, you speak that which we know well: nay, even of ourselves we know that your wisdom and understanding is exceeding, and that you became a defender of the deathless ones from chill doom. And through your devising we are come back again from the murky gloom and from our merciless bonds, enjoying what we looked not for, O lord, son of Cronos. And so now with fixed purpose and deliberate counsel we will aid your power in dreadful strife and will fight against the Titans in hard battle.’

So he said: and the gods, givers of good things, applauded when they heard his word, and their spirit longed for war even more than before, and they all, both male and female, stirred up hated battle that day, the Titan gods, and all that were born of Cronos together with those dread, mighty ones of overwhelming strength whom Zeus brought up to the light from Erebus beneath the earth [Briareus and Cottus and Gyes]. An hundred arms sprang from the shoulders of all [three] alike [therefore their appelation, hecatoncheires or hundred-handed], and each had fifty heads growing upon his shoulders upon stout limbs. These, then, stood against the Titans [who were their brothers] in grim strife, holding huge rocks in their strong hands. And on the other part, the Titans eagerly strengthened their ranks, and both sides at one time showed the work of their hands and their might. The boundless sea rang terribly around, and the earth crashed loudly: wide Heaven was shaken and groaned, and high Olympus reeled from its foundation under the charge of the undying gods, and a heavy quaking reached dim Tartarus and the deep sound of their feet, in the fearful onset, and of their hard missiles. So, then, they launched their grievous shafts upon one another, and the cry of both armies as they shouted reached to starry heaven; and they met together with a great battle-cry.

Then Zeus no longer held back his might; but straight his heart was filled with fury and he showed forth all his strength. From Heaven and from Olympus he came forthwith, hurling his lightning: the bolt flew thick and fast from his strong hand together with thunder and lightning, whirling an awesome flame. The life-giving earth crashed around in burning, and the vast wood crackled loud with fire all about. All the land seethed, and Ocean’s streams and the unfruitful sea. The hot vapour lapped round the earthborn Titans: flame unspeakable rose to the bright upper air: the flashing glare of the thunder-stone and lightning blinded their eyes for all their strength. Astounding heat seized Chaos: and to see with eyes and to hear the sound with ears it seemed even as if Earth and wide Heaven above came together; for such a mighty crash would have arisen if Earth were being hurled to ruin, and Heaven from on high were hurling her down; so great a crash was there while the gods were meeting together in strife. Also the winds brought rumbling earthquake and duststorm, thunder and lightning and the lurid thunderbolt, which are the shafts of great Zeus, and carried the clangour and the warcry into the midst of the two hosts. An horrible uproar of terrible strife arose: mighty deeds were shown and the battle inclined. But until then, they kept at one another and fought continually in cruel war.

And amongst the foremost Cottus and Briareos and Gyes insatiate for war raised fierce fighting: three hundred rocks, one upon another, they launched from their strong hands and overshadowed the Titans with their missiles, and buried them beneath the wide-pathed earth, and bound them in bitter chains when they had conquered them by their strength for all their great spirit, as far beneath the earth to Tartarus.
(Hesiod, Theogony, 617ff)