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place in post-war England, and they specifically bring in references to Tolkien's legendarium (at that time largely unpublished) and treats these references as primary fact within Lewis's fiction.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:
Joy Davidman
Davidman had become interested in C. S. Lewis while still in America. She first met him in August 1952, when she made a trip to the United Kingdom, after a two-year correspondence with him. She planned to finish her book on the Ten Commandments that she had been working on, and which showed influences of Lewis's style of apologetics. After several lunch meetings and walks accompanying Davidman and his brother, Warren Lewis wrote in his diary that "a rapid friendship" had developed between his younger brother and Davidman, whom he described as "a Christian convert of Jewish race, medium height, good figure, horn rimmed specs, quite extraordinarily uninhibited." She spent Christmas and a fortnight at The Kilns with the brothers. Though Davidman was deeply in love with Lewis there was no reciprocation on his side.