The "Tristan chord," first heard in Wagner's opera "Tristan und Isolde," is a mystifying collection of notes that defied traditional harmony during the 19th century. Its ambiguous tonality and unresolved tension dramatically influenced the course of Western classical music, opening pathways to modern dissonance and atonality. This chord symbolized a shift from the strictly structured compositions of the past to a new, emotive soundscape, exemplifying how a single harmonic idea can ripple through time and alter music history. What musical innovations have piqued your interest? Share your discoveries!