Belegaer is the fictional sea that lies west of Middle-earth in J.R.R. Tolkien’s legendarium.
Belegaer, also called the Great Sea, separates Middle-earth from Aman, the realm to the west. It is one of the major geographical features of Tolkien’s world and appears in accounts covering several ages of its history. The sea is associated with voyages, exile, return, and the changing shape of the world.
Its name can be confused with other geographical terms in Tolkien’s maps. Rhûn refers to the eastern region of Middle-earth, while Núrnen is an inland sea in Mordor. Cuiviénen is a body of water associated with the awakening of the Elves, not the great western ocean.
In Tolkien’s world history, the geography of the seas changes dramatically after the downfall of Númenor. The old world is reshaped, and Aman is removed from the ordinary physical world. Belegaer nevertheless remains a key term for the western sea in descriptions of the earlier geography.