Short answers, pulled from the story.
Led Zeppelin recorded the song on the 29th of January 1971 using the Rolling Stones Mobile studio unit. Engineer Andy Johns captured the performance during this session at Headley Grange.
The lyrics contain direct references to J.R.R. Tolkien's fantasy novel The Lord of the Rings. Scholars note allusions to Mordor and events from The Silmarillion within the track.
Robert Plant invited Sandy Denny to provide female vocals for the recording. She received three pyramids on the album sleeve as payment for her contribution.
This shorter track runs four minutes thirteen seconds compared to the five minute fifty-one second original. It exists alongside the standard version on remastered deluxe editions.
Led Zeppelin performed the song during their 1977 North American Tour with John Paul Jones singing Sandy Denny's vocal parts. Fairport Convention later performed the track with Robert Plant and Kristina Donahue at Cropredy Convention on the 9th of August 2008.