Give 'Em Enough Rope, for all of its many attributes, was essentially a holding pattern for the Clash, but the double-album London Calling is a remarkable leap forward, incorporating the punk aesthetic into rock & roll mythology and roots music. Before, the Clash had experimented with reggae, but that was no preparation for the dizzying array of styles on London Calling. There's punk and reggae, but there's also rockabilly, ska, New Orleans R&B, pop, lounge jazz, and hard rock; and while the record isn't tied together by a specific theme, its eclecticism and anthemic punk function as a rallying call. While many of the songs -- particularly "London Calling," "Spanish Bombs," and "The Guns of Brixton" -- are explicitly political, by acknowledging no boundaries the music itself is political and revolutionary. But it is also invigorating, rocking harder and with more purpose than most albums, let alone double albums. Over the course of the record, Joe Strummer and Mick Jones (and Paul Simonon, who wrote "The Guns of Brixton") explore their familiar themes of working-class rebellion and antiestablishment rants, but they also tie them in to old rock & roll traditions and myths, whether it's rockabilly greasers or "Stagger Lee," as well as mavericks like doomed actor Montgomery Clift. The result is a stunning statement of purpose and one of the greatest rock & roll albums ever recorded.