§ Of Tuor and the Fall of Gondolin The Silmarillion

But Morgoth thought that his triumph was fulfilled, recking little of the sons of Fëanor, and of their oath, which had harmed him never and turned always to his mightiest aid; and in his black thought he laughed, regretting not the one Silmaril that he had lost, for by it as he deemed the last shred of the people of the Eldar should vanish from Middle-earth and trouble it no more. If he knew of the dwelling by the waters of Sirion, he gave no sign, biding his time, and waiting upon the working of oath and lie. Yet by Sirion and the sea there grew up an Elven-folk, the gleanings of Doriath and Gondolin; and from Balar the mariners of Círdan came among them, and they took to the waves and the building of ships, dwelling ever nigh to the coasts of Arvernien, under the shadow of Ulmo's hand.