What was Númenor in J.R.R. Tolkien’s legendarium?

Númenor was an island kingdom in J.R.R. Tolkien’s legendarium.

Númenor, also called Westernesse, was a great island realm located in the ocean between Middle-earth and Aman. The Valar raised it from the sea for the Edain, the Men who had fought against Morgoth in the First Age. Its people were known as the Númenóreans, or Dúnedain.

The kingdom flourished for centuries, but its rulers became increasingly fearful of death and jealous of the immortal Elves. Under the influence of Sauron, King Ar-Pharazôn attacked Aman. The Valar appealed to Ilúvatar, who changed the shape of the world and drowned Númenor in the Downfall.

Survivors led by Elendil founded the realms of Arnor and Gondor. Númenor is therefore both a lost civilization and the ancestral source of important human kingdoms in The Lord of the Rings.