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place in post-war England, and they specifically bring in references to Tolkien's legendarium (at that time largely unpublished) and treats these references as primary fact within Lewis's fiction.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:
The House of the Wolfings
"The House of the Wolfings" was one of the influences on J. R. R. Tolkien's popular "The Lord of the Rings". In a December 31, 1960 letter published in "The Letters of J. R. R. Tolkien", (p. 303), Tolkien wrote: 'The Dead Marshes and the approaches to the Morannon owe something to Northern France after the Battle of the Somme. They owe more to William Morris and his Huns and Romans, as in "The House of the Wolfings" or "The Roots of the Mountains"." Among the numerous parallels with "The Lord of the Rings", Morris has Old English-style placenames such as Mirkwood (p. 2) and the Mark (title page), Germanic personal names such as Thiodolf (p. 8), and dwarves as skilled smiths ("How the Dwarf-wrought Hauberk was Brought away from the Hall of the Daylings", p. 97).