The Glanduin was a river in the region of Eriador in Middle-earth and a northern arm of the Gwathló. Beginning in the Hithaeglir south of Khazad-dûm, it flowed west-north-west until it was met by the Sirannon near the old location of Ost-in-Edhil, the capital of the Ñoldor of Eregion (Hollin). From there the Glanduin flowed towards the Mitheithel, which it met in the marshes known as Swanfleet or Nîn-in-Eilph north-east of Tharbad. From there on both rivers became the Gwathló. It was approximately seventy-five miles in length.