Tam Lin - Fairport Convention (1969)
Folk Rock has often used traditional source material to create an electric spin on an ancient song. The Byrds did it with "John Riley". Steeleye Span brought the 13th century murder ballad "Little Sir Hugh" into the modern age. In recent years, Ween updated "The Unquiet Grave" into "Cold Blows The Wind", a gothic masterpiece. However, none have capitalized on the word "rock" in the term better than Fairport Convention on this retelling of a 14th century epic poem from Scotland. Sandy Denny sings as if her life depended on it. Richard Thompson's power chords rip through the sword and sorcery motif while David Swarbrick's fiddle accents the fills of this seven minute power house. Colin Meloy of the Decemberists has said that the song was a huge influence on his own Hazards of Love album. Amazingly, all the moods encapsulated in that 39 minute rock opera pour through this one song. I was floored the first time I heard it, listening to Leige & Lief on a dark night while driving the Blue Ridge Parkway. Even without the location, I know you will be too (But take your laptop out into the woods at midnight for full effect!).
Also, hit up You Ain't No Picasso for a faithful live cover by the Decemberists, featuring Petra Haden on lead vocals!