The northwestern portion of Middle-Earth throughout the Ages of
the Stars and the First Age of the Sun, Beleriand was made up of
several regions including Hithlum, Doriath, and Nevrast. In the
north of Beleriand, was Uttumno and Thangorodrim where lived Morgoth.
The focus of The Silmarillion, most probably written by Bilbo Baggins,
was in Beleriand, as were most of the battles and wars making up
the struggle to regain the Silmarils. Beleriand was destroyed and
sank beneath the waves at the end of the First Age of the Sun, during
the struggle between the Valar and Morgoth. The only parts of Beleriand
to survive, apart from some islands made up of mountaintops were
Lindon and some parts of the Blue Mountains, the Ered Luin.