Middle-earth
Another example is C. S. Lewis's "Space Trilogy," in which Earth is also called Middle-earth. Lewis's novels are situated at the approximate time of World War II, with the last novel, "That Hideous Strength," taking place in post-war England, and they specifically bring in references to Tolkien's legendarium (at that time largely unpublished) and treats these references as primary fact within Lewis's fiction. Merlin, of King Arthur fame, is treated as a successor to the Atlantis magic found within "Numinor" (Lewis's unintentional misspelling of Númenor), and similarities can also be found in the Quenya name for Númenor, which is "Atalantë," and Lewis specifically references the earth as Middle-earth twice, both in Chapter 13, "They Have Pulled Down Deep Heaven on Their Heads". Lewis's borrowings came directly from Tolkien himself: they were close friends and shared each other's literary creations. Lewis encouraged Tolkien to persevere with his Middle-earth writings.A small selection from the many books about Tolkien and his created world:
Cecil Harwood
Cecil Harwood was the youngest of five children born into the household of a pastor. He attended school together with Owen Barfield, who became his life-long friend and co-worker in many areas of his life. Together they studied at Oxford University and were part of the circle of the Inklings that included C.S. Lewis and J.R.R Tolkien. His friendship with Daphne Olivier, who later became his wife, led him to meet Rudolf Steiner and subsequently, to found the first Waldorf school in England, the so-called “New School” that later became Michael Hall, together with her and three other colleagues. He remained connected to the school for the rest his life.