The River Teiglin began in the Ered Wethrin on he borders of Dor-lómin. From there the river flowed southeast into the Forest of Brethil and then south where it became the River Sirion.

There were two important parts to the River Teiglin. One of those was the Crossings of Teiglin where a road ran across the river heading for Minas Tirith of Sirion. The other important part of the river was the Ravines of Teiglin. It was from these ravines on the borders of the Forest of Brethil that Túrin was able to get beneath the dragon, Glaurung, and slay him.