Sirion

The river

Sirion rose at Eithel Sirion on the eastern face of the Ered Wethrin, where Fingolfin built his fortress, and flowed first east and then south. In its upper course it ran through the Pass of Sirion between the Ered Wethrin and the western spurs of Dorthonion, a narrow way guarded by the isle of Tol Sirion. South of the pass the river received the Teiglin on the west and the Esgalduin on the east, flowing along the western border of Doriath and past the forest of Brethil. Then it spread into the great marshes and meres of Aelin-uial, fell over the Andram at the Gates of Sirion, and disappeared underground for some leagues before emerging again to run south through Nan-tathren to the delta on the Bay of Balar, the Mouths of Sirion.

Ulmo's river

Of all the waters of Middle-earth, Sirion was the one in which Ulmo kept most of his power after the Valar withdrew to Aman. Through it he watched Beleriand and sent his counsel to the Noldor: the dreams that led to the founding of Gondolin and Nargothrond, the messages carried to Turgon, the warning delivered to Tuor. Ulmo laid a veil of mists about the vale to hide the entrance to Gondolin, and the Elves of the hidden city entered and left by the river. When the Eldar fled to the Mouths at the end, it was Ulmo's protection that let them survive there for a time.

The road of war

The Pass of Sirion was the gate between the north and the heart of Beleriand. Finrod built Minas Tirith on Tol Sirion to hold it; Sauron took it after the Bragollach and made it the Isle of Werewolves; Lúthien and Huan freed it. At the Nirnaeth the western host fought in the Fen of Serech at the pass's northern end, and Huor died there. Later, Beleg and Gwindor followed the orcs' road down the vale, and Túrin's outlaws and Gwindor and Túrin passed along it to Nargothrond. Sirion vanished beneath the sea with the rest of Beleriand at the end of the Age.