Lewis provided a timeline of events related to The Chronicles of Narnia, in emulation of "The Tale of the Years" chronology in J. R. R. Tolkien's "The Lord of the Rings". He gave an "Outline of Narnian History" in manuscript form to Walter Hooper, who included it in his essay "Past Watchful Dragons: The Fairy Tales of C. S. Lewis". The novels never explicitly mention the year or years in which events take place, so the timeline is the only source for this information. Kathryn Lindskoog, along with other Lewis scholars, has challenged the authenticity of some posthumous works attributed to Lewis and edited by Hooper, but the validity of the outline in particular has not been questioned. The outline is accepted by Lewis experts and has been included in works by Paul Ford, Martha Sammons and others.