In my previous post, I related how by the guidance of Ulmo, Turgon discovered the hidden vale of Tumladen and thought how he might build a fair city, a memorial of ancient Tirion, for which he yearned in exile. After the Dagor Aglareb, the unquiet that Ulmo set in his heart when he journeyed with Finrod Felagund in the Vales of Sirion returned to him, and summoning the most skilled of his people, he went forth from Nevrast in secret and began a long and secret labour. Sentinals he set around that hidden valley in the Encircling Mountains, so that none would mark their passing, or their work, and they were protected by Ulmo. When the city was full-wrought, Turgon removed from his halls at Vinyamar by the sea and went with a great many people, Noldor and Sindar, to the Hidden City. Ondolindë it was called in the High Elven tongue, which signified ''The Rock of the Music of Water,'' but it was called Gondolin in the Sindarin tongue, the Hidden Rock.
Before he departed, Ulmo appeared to Turgon and 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 Eldalië 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 too lay under the Doom of Mandos, and that maybe one day treason would find its way even into the Mountains, and they would be in peril of fire. But Ulmo also foretold the coming of someone to warn Turgon even from Nevrast, and told him therefore to leave arms and a sword in his house so that when that day came, he would know the one sent by Ulmo and not be deceived. And so Turgond departed, and came unseen to Gondolin and the mountains were shut behind him.
Of surpassing beauty was Gondolin, a veritable memorial of Tirion the Fair over Sea. Tolkien describes the city thus:
''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.'' (The Silmarillion, Chapter XV, Of the Noldor in Beleriand).
The above image (by Ted Nasmith) depicts Gondolin. The man standing on the right is Tuor.