§ Of Tuor and the Fall of Gondolin The Silmarillion

Then Turgon pondered long the counsel of Ulmo, and there came into his mind the words that were spoken to him in Vinyamar: '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.' But Turgon was become proud, and Gondolin as beautiful as a memory of Elven Tirion, and he trusted still in its secret and impregnable strength, though even a Vala should gainsay it; and after the Nirnaeth Arnoediad the people of that city desired never again to mingle in the woes of Elves and Men without, nor to return through dread and danger into the West. Shut behind their pathless and enchanted hills they suffered none to enter, though he fled from Morgoth hate-pursued; and tidings of the lands beyond came to them faint and far, and they heeded them little. The spies of Angband sought for them in vain; and their dwelling was as a rumour, and a secret that none could find. Maeglin spoke ever against Tuor in the councils of the King, and his words seemed the more weighty in that they went with Turgon's heart; and at the last he rejected the bidding of Ulmo and refused his counsel. But in the warning of the Vala he heard again the words that were spoken before the departing Noldor on the coast of Araman long ago; and the fear of treason was wakened in Turgon's heart. Therefore in that time the very entrance to the hidden door in the Encircling Mountains was caused to be blocked up; and thereafter none went ever forth from Gondolin on any errand of peace or war, while that city stood. Tidings were brought by Thorondor Lord of Eagles of the fall of Nargothrond, and after of the slaying of Thingol and of Dior his heir, and of the ruin of Doriath; but Turgon shut his ear to word of the woes without, and vowed to march never at the side of any son of Fëanor; and his people he forbade ever to pass the leaguer of the hills.