The Classical and early Romantic eras witnessed a gradual expansion in the scope of the cadenza, which tended to adopt a more significant structural role by incorporating relevant thematic material from the movement rather than comprising mere cadential elaboration. In the first movement in particular, the cadenza fulfilled both an architectural function, with its climactic passage for the soloist balancing the orchestral ritornello, and a dramatic one of allowing the soloist free rein for unfettered solo display. Originally improvisations or passages intended to sound like improvisations, some cadenzas were actually written out by composers either for use in performance or as models for students to imitate. Most of the authentic cadenzas by Mozart for his piano concertos and, to a certain extent, the written-out cadenza in his Sinfonia Concertante K.364 serve as excellent models of the Classical cadenza. Although their content is varied and imaginative, the majority of Mozart's surviving piano concerto cadenzas (with the exception of some second- and third-movement examples) typically adopt a tripartite design, bound together, as it were, in one harmonic progression. The first (and largest) subdivision normally commenced either with one of the principal themes of the movement (e.g. K.453, first movement), with the figure heard during the cadential preparation, or with an energetic virtuoso flourish, which may also have thematic affinities (e.g. K.271 first movement), emanating from the harmonic tension of the initial tonic six-four chord.