How did Symphonie fantastique influence Franz Liszt and Richard Wagner?

Hector Berlioz’s Symphonie fantastique (1830) was a landmark in 19th-century music, profoundly influencing both Franz Liszt and Richard Wagner through its innovative use of the idée fixe—a recurring theme that unifies a work dramatically and musically.12

Influence on Franz Liszt
Liszt was deeply impacted by the symphony, which he famously transcribed for piano in 1833. From Berlioz, Liszt inherited a command of the Romantic orchestra and a penchant for "diabolic" musical qualities. Berlioz’s idée fixe served as a direct precursor to Liszt’s own techniques of thematic transformation, where a single musical idea is altered to suit different contexts, as seen in his Faust Symphony.312

Influence on Richard Wagner
Wagner’s development of the leitmotif—a central element of his music dramas—is considered an extension of Berlioz’s idée fixe. Furthermore, Wagner’s masterful use of instrumental color and his ability to integrate diverse compositional techniques into large-scale structures were influenced by the pioneering orchestration and programmatic innovations established by Berlioz in the Symphonie fantastique.124