Queen Jadis rules the destroyed world of Charn in C.S. Lewis’s The Magician’s Nephew.
The novel, published in 1955, serves as a prequel to the other Chronicles of Narnia stories in its internal chronology. Its characters Digory Kirke and Polly Plummer travel between worlds using magical objects and eventually witness the creation of Narnia.
Charn is presented as an ancient world whose civilization has been destroyed. Jadis, its last queen, awakens after a long enchantment and brings about the end of the world through a destructive act. Her later arrival in Narnia explains how the White Witch enters that world.
Charn is not another name for Narnia. Narnia is the newly created land ruled by Aslan, while Charn is the bleak, abandoned world connected to Jadis’s earlier history. Archenland and Calormen are separate countries within the Narnian world.