Númenor is the island kingdom that sinks beneath the sea in J.R.R. Tolkien’s legendarium. Its downfall is one of the central events in the Second Age of Middle-earth’s history.
The island was raised from the sea by the Valar and given to the Edain who had aided the Elves and opposed Morgoth during the First Age. Númenóreans enjoyed long lives and became powerful sailors, but their relationship with the immortal Eldar and the Valar eventually deteriorated.
Sauron exploited Númenórean fear of death. After being taken to the island as a prisoner, he gained influence over King Ar-Pharazôn and encouraged the Númenóreans to challenge the Ban of the Valar. Their attempted invasion of the Undying Lands brought catastrophic punishment: the island was destroyed and submerged.
Elendil and his sons survived because they opposed the king’s policy. They founded the realms of Arnor and Gondor in Middle-earth. Númenor is therefore both a lost civilization and the ancestral source of the Men who later resist Sauron.