Eä in the context of "The Silmarillion"

In J. R. R. Tolkien's legendarium, the history of Arda, also called the history of Middle-earth, began when the Ainur entered Arda, following the creation events in the Ainulindalë and long ages of labour throughout Eä, the fictional universe. Time from that point was measured using Valian Years, though the subsequent history of Arda was divided into three time periods using different years, known as the Years of the Lamps, the Years of the Trees, and the Years of the Sun. A separate, overlapping chronology divides the history into 'Ages of the Children of Ilúvatar'. The first such Age began with the Awakening of the Elves during the Years of the Trees and continued for the first six centuries of the Years of the Sun. All the subsequent Ages took place during the Years of the Sun. Most Middle-earth stories take place in the first three Ages of the Children of Ilúvatar.

Major themes of the history are the divine creation of the world, followed by the splintering of the created light as different wills come into conflict. Scholars have noted the biblical echoes of God, Satan, and the fall of man here, rooted in Tolkien's own Christian faith. Arda is, as critics have noted, "our own green and solid Earth at some quite remote epoch in the past." As such, it has not only an immediate story but a history, and the whole thing is an "imagined prehistory" of the Earth as it is now.

The Ainulindalë (Quenya: [ˌai̯nuˈlindalɛ]; "Music of the Ainur") is the creation account in J. R. R. Tolkien's legendarium, published posthumously as the first part of The Silmarillion in 1977. The Ainulindalë sets out a central part of the cosmology of Tolkien's legendarium, telling how the Ainur, a class of angelic beings, perform a great music prefiguring the creation of the material universe, Eä, including Middle-Earth.The creator Eru Ilúvatar introduces the theme of the sentient races of Elves and Men, not anticipated by the Ainur, and gives physical being to the prefigured universe. Some of the Ainur decide to enter the physical world to prepare for their arrival, becoming the Valar and Maiar.

Tolkien wrote the initial version of the Ainulindalë between November 1919 and the spring of 1920 as "Music of the Ainur", and then completely rewrote it in 1930. He continued to make further revisions throughout his life. The early version was eventually published by his son Christopher in The Book of Lost Tales 1.

The geography of Middle-earth encompasses the physical, political, and moral geography of J. R. R. Tolkien's fictional continent Middle-earth on the planet Arda, but widely taken to mean all of creation (Eä) as well as all of his writings about it. Arda was created as a flat world, incorporating a Western continent, Aman, which became the home of the godlike Valar, as well as Middle-earth. At the end of the First Age, the Western part of Middle-earth, Beleriand, was drowned in the War of Wrath. In the Second Age, a large island, Númenor, was created in the Great Sea, Belegaer, between Aman and Middle-earth; it was destroyed in a cataclysm near the end of the Second Age, in which Arda was remade as a spherical world, and Aman was removed so that Men could not reach it.

In The Lord of the Rings, Middle-earth at the end of the Third Age is described as having free peoples, namely Men, Hobbits, Elves, and Dwarves in the West, opposed to peoples under the control of the Dark Lord Sauron in the East. Some commentators have seen this as implying a moral geography of Middle-earth. Tolkien scholars have traced many features of Middle-earth to literary sources such as Beowulf, the Poetic Edda, or the mythical Myrkviðr. They have in addition suggested real-world places such as Venice, Rome, and Constantinople/Byzantium as analogues of places in Middle-earth. The cartographer Karen Wynn Fonstad has created detailed thematic maps for Tolkien's major Middle-earth books, The Hobbit, The Lord of the Rings, and The Silmarillion.