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.
Tolkien meant Arda to be 'our own green and solid Earth', seen here in the Baltistan mountains, 'at some quite remote epoch in the past'.
