Ossiriand was called the ‘Land of Seven Rivers,’ and was also known as Lindon during the First Age. It was called the 'Land of Music' by the Noldor.

It was a forested region east of Beleriand through which ran the River Gelion and its six tributaries, Ascar, Thalos, Legolin, Brilthor, Duilwen, Adurant. Ossiriand was 60 leagues long by 50 broad at its widest. Its northern boundary was the Ascar and its southern the Adurant with its island of Tol Galen.

The Nandor, led by Denethor I, dwelt here when they came northwards to the realm of Thingol. When Denethor son of Lenwë was killed, many of the Nandor remained in Ossiriand without a king and became known as the Laiquendi, or Green-elves.

In the midst of the River Adurant, in the south of Ossiriand, was Tol Galen, a green island where Beren and Lúthien came to live as mortals after returning to Middle-earth. Their son, Dior, also lived in Ossiriand for a time at Lanthir Lamath.

It was into the north of Ossiriand that the race of Men first came. They wandered over its mountains and camped near the rivers, and they were discovered there by Finrod Felegund.

In the War of Wrath, at the end of the First Age, most of Ossiriand was drowned by the Great Sea. The regions that remained intact were renamed Harlindon and Forlindon.
Encyclopedia entry originally written by Ringhilwen