River in western Beleriand, which runs close to Nargothrond. It provided a natural defence for this city against the forces of Morgoth, which mostly fear water. That is, until Turin foolishly advised the elves to build a bridge, which provided a handy access route for Glaurung...
It's featured in Tolkien's book The Silmarillion - see the map at the back for exact details of where it goes.
av Andy 11. mai 2004