Tolkien stated that the core theme of The Lord of the Rings was death and the human desire to escape it. The theme, which recurs throughout the work, is sharply visible in an appendix, The Tale of Aragorn and Arwen, in which the immortal Elf Arwen chooses mortality so that she can marry the mortal Man Aragorn. The result, as with the earlier intermarriage of their ancestors Lúthien and Beren in the First Age in Beleriand, was to make Aragorn's line exceptionally long-lived among Men, and as the royal family intermarried with other people of Gondor, to maintain or extend the lifespan of the entire race.