This rock instrumental was recorded during sessions for Led Zeppelin III but remained unreleased until 2015, when it was included on the deluxe reissued version of Coda. Jimmy Page told Mojo: "'St. Tristan's Sword' is the sort of thing that we'd do when we were playing live, not that that track came out from a live thing. But we'd be doing stuff like that, veering off into something and then come back (into the main part of the song). I'd had the riff and the changes to that and I thought, 'Let's just try it.' There are two takes of it and that's it, then we moved on to something else. But it's got a little charm of its own. On this version of Coda, it works. It might not have ever come out otherwise."
The song was recorded in the same session as "Gallows Pole," and features a similar sounding drum tone.
There is no actual Saint Tristan. However the tragic story of the Arthurian knight Tristan's adulterous love for the Irish princess Iseult, predates and most likely influenced the famous romantic tale of Lancelot and Guinevere.