Tolkien provides readers six appendices to the text of The Lord of the Rings. Although the information is not necessary to understand the main story, they add details to the history and describe the fates of many of the characters. Appendix A recounts the history of various rulers of Middle-earth, including the kings of Númenor and their descendants, the kings and stewards of Gondor, the rulers of Rohan, and the dwarves. This appendix also provides the complete history of Aragorn and Arwen's romance, including Elrond's initial disapproval.
Appendix B gives a chronology of major events. It begins with the most significant occurrences of the First and Second Ages, followed by a more detailed summary of the Third Age. The events of The Lord of the Rings are listed by specific date, and significant events in the lives of the characters after the end of the story are noted. Merry becomes Master of Buckland and Pippin becomes the Took, both heads of their families. Sam is elected Mayor. Aragorn brings his court north to visit occasionally and keeps in contact with the hobbits. Eventually, Sam passes the Red Book to his daughter and goes to the Havens, where the last Ringbearer also sailed to the Undying Lands. Merry and Pippin travel at last to Gondor and are laid to rest beside Aragorn. After Aragorn dies, Legolas and Gimli set sail, the last of the Fellowship to leave Middle-earth.
Appendix C provides the family trees of Frodo, Pippin, Merry and Sam, while Appendix D explains the Shire calendar and its relationship to the calendars of elves and men. Appendix E explains pronunciation and forms of writing. Appendix F explains the languages and races of Middle-earth during the time of the story, as well as commenting on some of the difficulties of translating all of these languages into modern English for today's readers.
Like the Prologue, the Appendices include material that adds to the depth of Middle-earth and elaborates the stories of individual characters, but would have slowed down the main narrative too much to be included there. It is possible to read, enjoy and understand The Lord of the Rings without this information, but the Appendices reward the reader with enhanced understanding of the characters, history, and culture of Middle-earth.
The most practically useful Appendix is the chronology, which helps the reader correlate events between the various storylines. For example, we learn that on March 7, 3019, Frodo arrives at the hidden fortress of Henneth Annûn — described in Book 4, Chapter 5, of The Two Towers — on the same day that Aragorn reaches Dunharrow to take the Paths of the Dead — described in Book 5, Chapter 2, of The Return of the King. Although happening at the same time, the two events occur roughly 150 pages apart in the narrative.
The story of Aragorn and Arwen describes his youth in Rivendell and the course of their meeting and courtship. For love of Aragorn, Arwen becomes only the second elf to abandon her immortality. The end of the tale, which recounts Aragorn's death and Arwen's grief, strongly evokes the sense of sacrifice and loss that pervades the trilogy. While Aragorn accepts his death peacefully, becoming "an image of the splendour of the Kings of Men in glory undimmed," Arwen resists both his death and her own: "She was not yet weary of her days, and thus she tasted the bitterness of the mortality that she had taken upon her." Her death, in Lothlórien, marks the end of the elves in Middle-earth and the loss of that special sense of magic, delight, and majesty that they represent.
This theme of loss, the sense that some must sacrifice themselves and their happiness in order to preserve the hope of happiness for others, is a central theme of Tolkien's work. The story of Arwen reinforces the conclusion of the main novel, when Frodo leaves Middle-earth along with the elves and Gandalf. They have saved the world, but not for themselves.