I came by a short chain of links to a medievalist's site A Clerk of Oxford. She has an excellent essay from a few years ago, C.S. Lewis the Medievalist: Baldr, Brunanburh, Athelstan, and Edmund the Just.
This is true on another level too, because - rather like the Canterbury Tales - the Narnia books are a compendium of literary genres, a joyous introduction to all the different kinds of things literature can do. The Magician's Nephew plays in the world of E. Nesbit's children's stories, The Horse and His Boy in the world of the Arabian Nights; Prince Caspian offers the dynastic conflicts of Shakespeare's history plays, its hero a fine Tudor prince properly educated in the quadrivium (!); The Voyage of the Dawn Treader is all Mandevillian 'Travels in the East', complete with sea-serpents and monopods; The Silver Chair starts with Middle English romance (Sir Orfeo and Sir Gawain and the Green Knight) and gets progressively more Norse as the story goes north, until we end up in the Prose Edda; and The Last Battle takes us to apocalypse by way of Brave New World.I had not thought of the series in quite that way, yet it makes some sense. I expect to explore the entire site.