Which Tolkien work was published posthumously in 1977 and describes the history of Arda?

The Tolkien work published posthumously in 1977 that describes the history of Arda is The Silmarillion.

The Silmarillion was edited and published by Tolkien’s son Christopher Tolkien after J.R.R. Tolkien’s death. It presents a collection of mythic histories covering the creation of the world, the divine beings known as the Valar, the Elves, and major conflicts against Morgoth.

Its central section, the Quenta Silmarillion, recounts the history of the Silmarils and the long struggles surrounding them. Other sections cover the creation of Eä, the shaping of Arda, the rise of Númenor, and events leading toward the stories of The Hobbit and The Lord of the Rings.

The book is not a conventional single-narrator novel. It gathers material from Tolkien’s many drafts and presents a deliberately historical, legendary style. Christopher Tolkien’s editorial work shaped the 1977 published form.