Rodgers told the story of the song to Uncut magazine: "One day he (Page) bought round a cassette and said, 'Would you like to write some lyrics to this?' It was 19 minutes long, it was absolutely fantastic! I said, 'I don't know that I can, can we shorten it?' So we got it down to nine minutes, and he was happy with the results. I said to him, 'It's funny, the chorus seems to have an extra bar in it.' And he goes, 'Well, it does. It's in 9/4.' That's the kind of thing he threw in with Led Zeppelin."