In the fiftieth year of the First Age, Turgon journeyed from his halls in Nevrast with his cousin Finrod. Ulmo guided him to the hidden valley of Tumladen, and there he founded Gondolin. The city was completed circa 126, and Turgon's people who had dwelt in Nevrast travelled there secretly.
The city was inviolate for almost four hundred years; Turgon did not break his secret leaguer until the time of the Nirnaeth Arnoediad in 471, and even after that disastrous battle he was able to return in secret to the city with the aid of Húrin Thalion.
Morgoth's servants finally discovered Gondolin through the treachery of Maeglin, and it was sacked in 510 (Main article: the Fall of Gondolin). Turgon was lost in the Fall of the city, but some few (including Tuor and Idril, with their child Eärendil) escaped the destruction and dwelt as Exiles at the Mouths of Sirion.