§ Of the Ruin of Beleriand and the Fall of Fingolfin The Silmarillion

Rumour came to Morgoth of these things, and he was unquiet amid his victories; and he desired greatly to learn tidings of Felagund and Turgon. For they had vanished out of knowledge, and yet were not dead; and he feared what they might yet accomplish against him. Of Nargothrond he knew indeed the name, but neither its place nor its strength; and of Gondolin he knew nothing, and the thought of Turgon troubled him the more. Therefore he sent forth ever more spies into Beleriand; but he recalled the main hosts of the Orcs to Angband, for he perceived that he could not yet make a final and victorious battle until he had gathered new strength, and that he had not measured rightly the valour of the Noldor nor the might in arms of the Men that fought beside them. Great though his victory had been in the Bragollach and in the years after, and grievous the harm that he had done to his enemies, his own loss had been no less; and though he held Dorthonion and the Pass of Sirion, the Eldar recovering from their first dismay began now to regain what they had lost. Thus Beleriand in the south had a semblance of peace again for a few brief years; but the forges of Angband were full of labour.