The Silmarillion

Because of the waywardness of Tilion, therefore, and yet more because of the prayers of Lórien and Estë, who said that sleep and rest had been banished from the Earth, and the stars were hidden, Varda changed her counsel, and allowed a time wherein the world should still have shadow and half-light. Anar rested therefore a while in Valinor, lying upon the cool bosom of the Outer Sea; and Evening, the time of the descent and resting of the Sun, was the hour of greatest light and joy in Aman. But soon the Sun was drawn down by the servants of Ulmo, and went then in haste under the Earth, and so came unseen to the east and there mounted the heaven again, lest night be over-long and evil walk under the Moon. But by Anar the waters of the Outer Sea were made hot and glowed with coloured fire, and Valinor had light for a while after the passing of Arien. Yet as she journeyed under the Earth and drew towards the east the glow faded and Valinor was dim, and the Valar mourned then most for the death of Laurelin. At dawn the shadows of the Mountains of Defence lay heavy on the Blessed Realm.

Varda commanded the Moon to journey in like manner, and passing under Earth to arise in the east, but only after the Sun had descended from heaven. But Tilion went with uncertain pace, as yet he goes, and was still drawn towards Arien, as he shall ever be; so that often both may be seen above the Earth together, or at times it will chance that he comes so nigh that his shadow cuts off her brightness and there is a darkness amid the day.

Therefore by the coming and going of Anar the Valar reckoned the days thereafter until the Change of the World. For Tilion tamed seldom in Valinor, but more often would pass swiftly over the western land, over Avathar, or Araman, or Valinor, and plunge in the chasm beyond the Outer Sea, pursuing his way alone amid the grots and caverns at the roots of Arda. There he would often wander long, and late would return.

Still therefore, after the Long Night, the light of Valinor was greater and fairer than upon Middle-earth; for the Sun rested there, and the lights of heaven drew nearer to Earth in that region. But neither the Sun nor the Moon can recall the light that was of old, that came from the Trees before they were touched by the poison of Ungoliant That light lives now in the Silmarils alone.

But Morgoth hated the new lights, and was for a while confounded by this unlooked-for stroke of the Valar. Then he assailed Tilion, sending spirits of shadow against him, and there was strife in Ilmen beneath the paths of the stars; but Tilion was victorious. And Arien Morgoth feared with a great fear, but dared not come nigh her, having indeed no longer the power; for as he grew in malice, and sent forth from himself the evil that he conceived in lies and creatures of wickedness, his might passed into them and was dispersed, and he himself became ever more bound to the earth, unwilling to issue from his dark strongholds. With shadows he hid himself and his servants from Arien, the glance of whose eyes they could not long endure; and the lands near his dwelling were shrouded in fumes and great clouds.

But seeing the assault upon Tilion the Valar were in doubt, fearing what the malice and cunning of Morgoth might yet contrive against them. Being unwilling to make war upon him in Middle-earth, they remembered nonetheless the ruin of Almaren; and they resolved that the like should not befall Valinor. Therefore at that time they fortified their land anew, and they raised up the mountain-walls of the Pelóri to sheer and dreadful heights, east, north, and south. Their outer sides were dark and smooth, without foothold or ledge, and they fell in great precipices with faces hard as glass, and rose up to towers with crowns of white ice. A sleepless watch was set upon them, and no pass led through them, save only at the Calacirya: but that pass the Valar did not close, because of the Eldar that were faithful, and in the city of Tirion upon the green hill Finarfin yet ruled the remnant of the Noldor in the deep cleft of the mountains. For all those of elven-race, even the Vanyar and Ingwë their lord, must breathe at times the outer air and the wind that comes over the sea from the lands of their birth; and the Valar would not sunder the Teleri wholly from their kin. But in the Calacirya they set strong towers and many sentinels, and at its issue upon the plains of Valmar a host was encamped, so that neither bird nor beast nor elf nor man, nor any creature beside that dwelt in Middle-earth, could pass that leaguer.