Music theory’s lasting fascination with tonal relationships based on major thirds has provided the motivation for countless inquiries. The inspiration for this project is no different, but the conclusion—that Romantic-era composers preferred some third relations over others—introduces a new angle to this field of study. Western composers’ predilection for the complex of keys including A-flat Major, C Major, and E Major crystallized in the music of the ‘New German School” compositions of Liszt and Wagner. This complex, in turn, formed the prototype for a compositional strategy whose echoes are audible in many Romantic compositions. By tracing the evolution of the complex from its diatonic underpinnings to its fully chromatic maturity, the bulk of this study attempts to establish both how the three keys—A-flat, C, and E—function together on multiple tonal levels, and why these specific keys were singled out for special treatment. Moreover, late-Romantic variations of the basic prototype will be discussed to support the notion that the A-flat-C-E complex remained a viable model for post-Wagnerian composers.