The Silmarillion

Again after a hundred years Glaurung, the first of the Urulóki, the fire-drakes of the North, issued from Angband's gates by night. He was yet young and scarce half-grown, for long and slow is the life of the dragons, but the Elves fled before him to Ered Wethrin and Dorthonion in dismay; and he defiled the fields of Ard-galen. Then Fingon prince of Hithlum rode against him with archers on horseback, and hemmed him round with a ring of swift riders; and Glaurung could not endure their darts, being not yet come to his full armoury, and he fled back to Angband, and came not forth again for many years. Fingon won great praise, and the Noldor rejoiced; for few foresaw the full meaning and threat of this new thing. But Morgoth was ill-pleased that Glaurung had disclosed himself over-soon; and after his defeat there was the Long Peace of wellnigh two hundred years. In all that time there were but affrays on the marches, and all Beleriand prospered and grew rich. Behind the guard of their armies in the north the Noldor built their dwellings and their towers, and many fair things they made in those days, and poems and histories and books of lore. In many parts of the land the Noldor and the Sindar became welded into one people, and spoke the same tongue; though this difference remained between them, that the Noldor had the greater power of mind and body. and were the mightier warriors and sages, and they built with stone, and loved the hill-slopes and open lands. But the Sindar had the fairer voices and were more skilled in music, save only Maglor son of Fëanor, and they loved the woods and the riversides; and some of the Grey-elves still wandered far and wide without settled abode, and they sang as they went.

Chapter 14 Of Beleriand and Its Realms

This is the fashion of the lands into which the Noldor came, in the north of the western regions of Middle-earth, in the ancient days; and here also is told of the manner in which the chieftains of the Eldar held their lands and the leaguer upon Morgoth after the Dagor Aglareb, the third battle in the Wars of Beleriand.

In the north of the world Melkor had in the ages past reared Ered Engrin, the Iron Mountains, as a fence to his citadel of Utumno; and they stood upon the borders of the regions of everlasting cold, in a great curve from east to west. Behind the walls of Ered Engrin in the west, where they bent back northwards, Melkor built another fortress, as a defence against assault that might come from Valinor; and when he came back to Middle-earth, as has been told, he took up his abode in the endless dungeons of Angband, the Hells of Iron, for in the War of the Powers the Valar, in their haste to overthrow him in his great stronghold of Utumno, did not wholly destroy Angband nor search out all its deep places. Beneath Ered Engrin he made a great tunnel, which issued south of the mountains; and there he made a mighty gate. But above this gate, and behind it even to the mountains, he piled the thunderous towers of Thangorodrim, that were made of the ash and slag of his subterranean furnaces, and the vast refuse of his tunnellings. They were black and desolate and exceedingly lofty; and smoke issued from their tops, dark and foul upon the northern sky. Before the gates of Angband filth and desolation spread southward for many miles over the wide plain of Ard-galen; but after the coming of the Sun rich grass arose there, and while Angband was besieged and its gates shut there were green things even among the pits and broken rocks before the doors of hell.

To the west of Thangorodrim lay Hísilóme, the Land of Mist, for so it was named by the Noldor in their own tongue because of the clouds that Morgoth sent thither during their first encampment; Hithlum it became in the tongue of the Sindar that dwelt in those regions. It was a fair land while the Siege of Angband lasted, although its air was cool and winter there was cold. In the west it was bounded by Ered Lómin, the Echoing Mountains that marched near the sea; and in the east and south by the great curve of Ered Wethrin, the Shadowy Mountains, that looked across Ard-galen and the Vale of Sirion.

Fingolfin and Fingon his son held Hithlum, and the most part of Fingolfin's folk dwelt in Mithrim about the shores of the great lake; to Fingon was assigned Dor-lómin, that lay to the west of the Mountains of Mithrim. But their chief fortress was at Eithel Sirion in the east of Ered Wethrin, whence they kept watch upon Ard-galen; and their cavalry rode upon that plain even to the shadow of Thangorodrim, for from few their horses had increased swiftly, and the grass of Ard-galen was rich and green. Of those horses many of the sires came from Valinor, and they were given to Fingolfin by Maedhros in atonement of his losses, for they had been carried by ship to Losgar.