Of the Noldor in Beleriand
Of the Noldor in Beleriand is the fifteenth chapter of the Quenta Silmarillion section within The Silmarillion.
Previously, the elf Turgon had been led by Ulmo to the secret vale of Tumladen, hidden within the Encircling Mountains. This was a vast plain of grass with a great hill in the middle, where he decided to build a city that was reminiscent of Tirion. Turgon returned to his realm of Nevrast with the knowledge of this hidden place, and began planning to construct a refuge that would be hidden from the knowledge of Morgoth.
After the Dagor Aglareb, Turgon led his people away from Nevrast back to Tumladen. There they began the construction of a great city upon the hill in the center of the plain. After fifty two years of secret toil and building they at last completed the city of Gondolin. This city was known only to Turgon and those of the Noldor who had followed him there. Before Turgon left Nevrast for the last time, Ulmo appeared to him again. He warned Turgon that though he would shield Turgon's final journey to Gondolin from prying eyes, he could not free Turgon from the Doom of Mandos that plagued the exiles. Gondolin would stand the longest of all the realms of the Noldor, but in the end it too must eventually fall. When that time would come, Ulmo would send Turgon a messenger to warn him of the impending doom. Ulmo bade Turgon to create unique armor and weapons for that messenger, who would come to Nevrast himself one day and take up the equipment. These would be a sign that the messenger was sent by Ulmo. Having done this, Turgon and his followers left Nevrast forever and went to Gondolin in secret.
Turgon prospered in Gondolin, which became a thriving city. Gondolin's location was kept secret from Morgoth throughout the wars against the Dark Power. Gondolin produced many works, like Glingal and Belthil, forged at the image of the Two Trees of Valinor. As for Nevrast, it decayed as the years went on, and no one inhabited the city again.
While Gondolin was being built, Finrod Felagund created his realm of Nargothrond, which would become a great city. His sister, Galadriel, would reside in the realm of Doriath. There Melian and she would often speak of Valinor, but Galadriel would never speak of what happened after the Darkening of Valinor began. But Melian was perceptive and wise, and she soon guessed that Galadriel was hiding something from her. Eventually, Galadriel admitted part of the truth, that the Noldor had not come as messengers of the Valar. However, she did not mention the First Kinslaying.
Melian told Thingol what Galadriel had said, and cautioned him to beware of the Sons of Fëanor. Soon, rumors of the Kinslaying did indeed reach the ears of Thingol. The truth being known to him at last, Thingol confronted Finrod and his brothers who happened to be in Doriath at the time. Finrod protested that it was Fëanor and his followers who had been the ones mainly responsible for the evils the Noldor had done, not Finrod and his party. But he allowed Angrod to tell the whole story of what had happened in the flight from Aman. Thingol's wrath towards Finrod and Fingolfin was softened by what he heard, but he did not forgive the sons of Fëanor. In vengeance, he forbade the usage of Quenya, the language of the Noldor, within the borders of Doriath. In later years, this would lead to the rise of Sindarin over Quenya, which would become an almost dead language outside of books and the private use of the exiles.
When Nargothrond was finished, a feast was held to celebrate its completion, and Galadriel came back from Doriath to celebrate. She asked Finrod why he was not married. Foresight seemed to come upon Finrod, and he said that one day he would swear an oath - Ring of Barahir - that one day he would have to fulfill no matter the consequences, and as a result no child would inherit his works.