The Lost Road
The Lost Road is an unfinished story by J.R.R. Tolkien in which he attemped to link the newly developed Numenor story of the Legendarium with the Ælfwine story of The Silmarillion as it then stood. It seems likely that it was written in 1935-6.
The original idea of the book came out of discussions that Tolkien had with C.S. Lewis who said that "There is too little of what we really like in stories" and they thus tried to write their own. C.S. Lewis took 'Space Travel' and his story emerged a few years later as "Out of the Silent Planet" Tolkien meanwhile took 'Time Travel' and wrote the Lost road.
The theme of the book is one of 'Preincarnation' That a father and son duo, sharing names that are etymologically connected with Elendil (Elf-friend) and Valandil (God-friend) Such as the pairs Ælfwine/Eadwine, Alboin/Audoin and the like. In the story the father son pair were to go back in time through different phases of the history of their names - in notes Tolkien lists them as 'Anglo Saxon. Irish legends. Prehistoric north. Belariand. Numenor.'
However, Tolkien only wrote 4 chapters of the story. The two opening chapters, and two which take place in Numenor. It seems he abandoned it due to his interest only in the 'Numenor bits' and possibly the fact that he was working on the Silmarillion at the time.
However, this was not the last time Tolkien tried to integrate the Numenor story into a time travel frame work, as he tried a second time a decade later with The Notion Club Papers