"Fertile Land" (*Pays fertile*) is a mysterious realm captured in several paintings by Paul Klee, as well as the title of an essay by the French composer and conductor Pierre Boulez; the essay explores the interplay between music and the visual arts within the theoretical writings and artistic practice of this European avant-garde genius. Raised in a family of a violinist and a singer, Klee possessed a profound understanding of classical musical forms and employed them to address purely painterly challenges. He frequently incorporated musical notation into his semi-abstract compositions, depicting conductors, singers, and imaginary instruments, while also drawing upon musical terminology in his lectures and titles—transforming, for instance, the temporal span of a fugue into the spatial dimension of a painting. Boulez, in turn, found a foundation in Klee’s art and theory for examining musical structure and rhythm. This continuous exchange—this transition between music, painting, and literature, as well as between theoretical rigor and expressive inspiration—constitutes, in Boulez’s view, the fertile land of all creative endeavor.