§ Of the Fifth Battle: Nirnaeth Arnoediad The Silmarillion

So it was that Turgon fought his way southward, until coming behind the guard of Húrin and Huor he passed down Sirion and escaped; and he vanished into the mountains and was hidden from the eyes of Morgoth. But the brothers drew the remnant of the Men of the house of Hador about them, and foot by foot they withdrew, until they came behind the Fen of Serech, and had the stream of Rivil before them. There they stood and gave way no more.