The subject matter of this song is Jim Morrison. It is a combination of a dream Patti Smith had about the late Doors singer and her visit to Morrison's grave in Père Lachaise Cemetery, Paris.
In Patti Smith's dream, she helps Jim Morrison, bound like Prometheus, to break free. She recalled in her lyric collection Complete:
"I had this dream. I came in on a clearing. There were natives in a circle bending and gesturing. I saw a man stretched across a marble slab. Jim Morrison. He was alive with wings that merged with the marble. Like Prometheus, he struggled, but freedom was beyond him. I stood over him chanting, break it up break it up break it up… The stone dissolved and he moved away. I brushed the feathers from my hair, adjusted my pillow, and returned to sleep."
This is about as close as Horses comes to a conventional hard rock track. It is therefore no surprise to learn that it was co-written with by Smith with Television's Tom Verlaine (who was then her lover). Verlaine also contributed guitar work to the track.