The Silmarillion

East of Dorthonion the marches of Beleriand were most open to attack, and only hills of no great height guarded the vale of Gelion from the north. In that region, upon the March of Maedhros and in the lands behind, dwelt the sons of Feanor with many people; and their riders passed often over the vast northern plain, Lothlann the wide and empty, east of Ard-galen, lest Morgoth should attempt any sortie towards Bast Beleriand. The chief citadel of Maedhros was upon the Hill of Himring, the Ever-cold; and that was wide-shouldered, bare of trees, and flat upon its summit, surrounded by many lesser hills. Between Himring and Dorthonion there was a pass, exceeding steep upon the west, and that was the Pass of Aglon, and was a gate unto Doriath; and a bitter wind blew ever through it from the north. But Celegorm and Curufin fortified Aglon and held it with great strength, and all the land of Himlad southward between the River Aros that rose in Dorthonion and his tributary Celon that came from Himring.

Between the arms of Gelion was the ward of Maglor, and here in one place the hills failed altogether: there it was that the Orcs came into East Beleriand before the Third Battle. Therefore the Noldor held strength of cavalry In the plains at that place; and the people of Caranthir fortified the mountains to the east of Maglor's Gap. There Mount Rerir, and about it many lesser heights, stood out from the main range of Ered Lindon westward; and in the angle between  Rerir and Ered Lindon there was a lake, shadowed by mountains on all sides save the south. That was Lake Helevorn, deep and dark, and beside it Caranthir had his abode; but all the great land between Gelion and the mountains, and between Rerir and the River Ascar, was called by the Noldor Thargelion, which signifies the Land beyond Gelion, or Dor Caranthir, the Land of Caranthir; and it was here that the Noldor first met the Dwarves. But Thargelion was before called by the Grey-elves Talath Rhunen, the East Vale.

Thus the sons of Feanor under Maedhros were the lords of East Beleriand, but their people were in that time mostly in the north of the land, and southward they rode only to hunt in the greenwoods. But there Amrod and Amras had their abode, and they came seldom northward while the Siege lasted; and there also other of the Elf-lords would ride at times, even from afar, for the land was wild but very fair. Of these Fin-rod Felagund came most often, for he had great love of wandering and he came even into Ossiriand, and won the friendship of the Green-elves. But none of the Noldor went ever over Ered Lindon, while their realm lasted; and little news and late came into Beleriand of what passed in the regions of the East.

Chapter 15

Of the Noldor in Beleriand It has been told how by the guidance of Ulmo Turgon of Nevrast discovered the hidden vale of Tumladen; and that (as was after known) lay east of the upper waters of Sirion, in a ring of mountains tall and sheer, and no living thing came there save the eagles of Thorondor. But there was a deep way under the mountains delved in the darkness of the world by waters that flowed out to join the streams of Sirion; and this way Turgon found, and so came to the green plain amid the mountains, and saw the island-hill that stood there of hard smooth stone; for the vale had been a great lake in ancient days. Then Turgon knew that he had found the place of his desire, and he resolved to build there a fair city, a memorial of Tirion upon Tuna; but he returned to Nevrast, and remained there in peace, though he pondered ever in his thought how he should accomplish his design.

Now after the Dagor Aglareb the unquiet that Ulmo set in his heart returned to him, and he summoned many of the hardiest and most skilled of his people, and led them secretly to the hidden vale, and there they began the building of the city that Turgon had devised; and they set a watch all about it, that none might come upon their work from without, and the power of Ulmo that ran in Sirion protected them. But Turgon dwelt still for the most part in Nevrast, until it came to pass that at last the city was full-wrought, after two and fifty years of secret toil. It is said that Turgon appointed its name to be Ondolinde in the speech of the Elves of Valinor, the Rock of the Music of Water, for there were fountains upon the hill; but in the Sindarin tongue the name was changed, and it became Gondolin, the Hidden Rock. Then Turgon prepared to depart from Nevrast and leave his halls in Vinyamar beside the sea; and there Ulmo came to him once again, and spoke with him. And he said: 'Now thou shalt go at last to Gondolin, Turgon; and I will maintain my power in the Vale of Sirion, and in all the waters therein, so that none shall mark thy going, nor shall any find there the hidden entrance against thy will. Longest of all the realms of the Eldalie shall Gondolin stand against Melkor. But love not too well the work of thy hands and the devices of thy heart; and remember that the true hope of the Noldor lieth in the West and cometh from the Sea.'

And Ulmo warned Turgon that he also lay under the Doom of Mandos, which Ulmo had no power to remove.

'Thus it may come to pass,' he said, 'that the curse of the Noldor shall find thee too ere the end, and treason awake within thy walls. Then they shall be in peril of fire. But if this peril draweth nigh indeed, then even from Nevrast one shall come to warn thee, and from him beyond ruin and fire hope shall be born for Elves and Men. Leave therefore in this house arms and a sword, that in years to come he may find them, and thus shalt thou know him, and not be deceived.' And Ulmo declared to Turgon of what kind and stature should be the helm and mail and sword that he left behind.

Then Ulmo returned to the sea, and Turgon sent forth all his people, even to a third part of the Noldor of Fingolfin's following, and a yet greater host of the Sindar; and they passed away, company by company, secretly, under the shadows of Ered Wethrin, and they came unseen to Gondolin, and none knew whither they had gone. And last of all Turgon arose, and went with his household silently through the hills, and passed the gates in the mountains, and they were shut behind him.

Through many long years none passed inward thereafter, save Hurin and Huor only; and the host of Turgon came never forth again until the Year of Lamentation after three hundred and fifty years and more. But behind the circle of the mountains the people of Turgon grew and throve, and they put forth their skill in labour unceasing, so that Gondolin upon Amon Gwareth became fair indeed and fit to compare even with Elven Tirion beyond the sea. High and white were its walls, and smooth its stairs, and tall and strong was the Tower of the King. There shining fountains played, and in the courts of Turgon stood images of the Trees of old, which Turgon himself wrought with elven-craft; and the Tree which he made of gold was named Glingal, and the Tree whose flowers he made of silver was named Belthil. But fairer than all the wonders of Gondolin was Idril, Turgon's daughter, she that was called Celebrindal, the Silver-foot, whose hair was as the gold of Laurelin before the coming of Melkor. Thus Turgon lived long in bliss; but Nevrast was desolate, and remained empty of living folk until the ruin of Beleriand.