Art-Rock/Progressive-Rock intend to expand the limits of rock & roll. Inspired by the Beatles' Sgt. Pepper, the first wave of Art-Rock musicians decided that the only way the genre could grow was if they could incorporate elements of European and classical music to rock. Early Art-Rock by and large consisted in multi-sectioned compositions (not songs) with long, complex instrumental passages driven by dramatic, grandiose flourishes. Often, technical prowess and overall conception was emphasized more than melody or songwriting, which is why the genre primarily focused on albums, since the extended running time gave the bands freedom to experiment musically and expand their ideas. Art-rockers also frequently wrote their music as a concept album or rock operas, with the intention for the entire record to be perceived as a larger work, not a series of songs. As the genre progressed, Art-Rockers that drew from jazz instead of classical emerged, but the genre never quite shook its fascination with European music. Experimental rock is tangentally related to Art-Rock. It shares many of the same traits as Art-Rock, particularly in how it self-consciously expands the boundaries of the genre, yet it is more challenging, noisy and unconventional. It has more to do with modern art, particularly the avant garde, than classical music and consequentally Experimental Rock isn't nearly as easy to assimilate as conventional Art-Rock.