Ossiriand was a region of eastern Beleriand.
The Seven Rivers were, from north to south:
- River Gelion
- River Ascar or Rathlóriel
- River Thalos
- River Legolin
- River Brilthor
- River Duilwen
- River Adurant, with Tol Galen
Along the northern shore of the Ascar ran the Dwarf-Road to Nogrod.
Ossiriand was a green and forested land, and it was populated by the Nandor. In the early First Age before the rise of the Moon, a part of the Telerin Elven people called Nandor entered Ossiriand under their leader Denethor, and were given permission by Thingol to settle the lands.
Ossiriand was the only part of Beleriand that survived the War of Wrath, but Belegaer the Great Sea broke through the mountain chain at the former riverbed of Ascar, creating the Gulf of Lhûn. In the Second Age and Third Age the former lands of Ossiriand and Thargelion were known as Lindon, where Rodnor Gil-galad and Círdan ruled.
- J.R.R. Tolkien, The Silmarillion, Of the Coming of the Elves and the Captivity of Melkor
- J.R.R. Tolkien, The Silmarillion, Of Beleriand and Its Realms