At a recent gallery show of his artwork, Roger Dean — best known for his lush and fantastical album covers for Yes in the 1970s — was enjoying the crowd when a man approached him and held out his hand to shake. "Mr. Dean, your work has changed my life," he said, "I have gleaned so many amazing, mystical secrets from looking at your album covers, can you tell me sort of what you meant by it." Dean, ever polite, tried to let the man down easily. "I didn't mean anything at all. It was just a good — looking album cover." His superfan, disillusioned, and possibly embarrassed, now turned nemesis, "Well, what do you know?" he angrily spat, "You're just the artist!" Despite his protestations, Dean might have taken some responsibility for contributing to casting a wide mystical net over an entire subgenre of music, known sometimes derogatorily as progressive rock. You are unlikely to find a prog-rocker who refers to their own music in those terms, but the term serves as a way to describe a movement in rock, one steering a massive ship away from the siren call of blues-based rock that had so long dominated popular music, toward a more English tradition of what Greg Lake of the supergroup Emerson, Lake and Palmer (ELP) described as "troubadour, medieval storytelling." Rock would inherit this mantle proudly, looking toward the mythology of the past — often heavily informed by occult images — to construct the sound of the future.

Psychedelic rock bands set the course, but in the 1970s, a new wave of bands looked beyond the drugginess of psychedelia to classical music as the true guide. Coupled with the instruments of the future—particularly Moog synthesizers — progressive rock crafted rock suites, with some songs clocking twenty minutes or more. Dean's paintings were otherworldly landscapes of floating islands and boulders, or stone structures rising up like trees. Largely unpopulated, save for the occasional butterfly/dragon hybrid, there were no aliens, elves, or wizards. His worlds might be long-dead civilizations, like the lifeless plains of Mars haunted by the once-thriving Martian societies in Ray Bradbury's Martian Chronicles, or future lands where people have taken to hibernating in the inexplicable constructions of their cities, endlessly waiting. Dean had perfected the merging of science fiction with mysticism, invoking the imagination of prog-rock listeners who were convinced there was some story or greater truth behind his art, and spent hours listening and poring over the album covers, meant to coexist in an ideological way.

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Prog-rock bands were particularly adept at presenting themselves as being purveyors of the strange and the paranormal. Emerson, Lake and Palmer's eponymous first album includes "The Three Fates," a suite comprised of "Clotho," "Lachesis," and "Atropos," which sounds like contemporary classical music. The Three Fates, or the Moirai, are of course the three sisters of Greek mythology who wove the destiny of human beings. They would become the model for the three incanting sisters in Shakespeare's Macbeth, the witches who toil over their cauldron, cooking up spells and schemes to upend the normal course of things. In every way it was an unconventional thing to find on a rock album, and smacked of intellectualism, the antipathy of rock. But Lake, who left King Crimson to join Keith Emerson and Greg Palmer to form ELP, thinks despite how big and complex progressive rock could and did become, it was still pop music. By all indications, though, it was pop music that presented itself as something much more arcane.

When production was complete on ELP's 1973 album, Brain Salad Surgery, the band agreed they needed a standout album cover, a design that would reflect the aura of the music, which includes the thirty-minute suite "Karn Evil 9," a science fiction epic about a despotic computer, written in part by Peter Sinfield, the scribe responsible for the lyrics of King Crimson's fantastical early songs. ELP's manager had seen the work of an artist in Zurich and suggested they visit his home. The artist was H. R. Giger, whose techno-fetish paintings had not yet become popularly known. (In 1979, Giger's vision would be seen by millions in the film Alien, for which he designed the look of the alien, as well as the fossil-like spaceship where its eggs are lying dormant.)

"It was like a horror museum," Lake recalls, upon visiting the artist's home. "But Giger himself is a very sweet, kind, gentle and very sort of softly spoken." The band was led into in dining room where the chairs and table were all carved with black-skull motif: "The whole thing was black. Black chairs, black table, black skulls." Giger showed them some drawings he thought would work well the music, with metal work and the ELP logo added. Lake insists if one looks carefully, there is a penis in the throat of the figure being "x-rayed."

It is the combination of the music and the cover that Lake explains is like a cocktail: "You can put certain elements into a glass and nothing happens. If you put one extra element in, the whole thing becomes effervescent." This is the alchemy of rock and roll, where the songs, lyrics, art, and even the band's logo can become a whole experience that you can hold in your hand when you hold an album.

Prog-rock's roots, being in European music rather than American traditions like the blues, found the genre nudging up against classical forms, which are often thought to be highbrow. But the history of classical music reveals this is not the case. Progressive rock sits more in the tradition of the Romantic composers of the late eighteenth and early nineteenth centuries. Like the Romantic poet and artists, Romantic composers were also excavating a past where they believed a more authentic human spirit dwelled with nature, where the supernatural was a shadow at the edges having never been completely exorcised by Christianity. Romantic composers wanted music to capture emotion and subjectivity. The composer and pianist Franz Liszt's rapturous performances caused audience members to swoon, and his "flamboyant" style likely influenced the keyboardists of progressive rock such as Keith Emerson and Rick Wakeman.

Progressive rock also found in the Romantic tradition what had been drawn from British folk music as a method for experimentation. Béla Bartók, one of the last of the Romantic composers, was enamored with the folk music of his native Hungary. As the writer Ivan Hewitt explains, "The wild irregular rhythms of Balkan dance encouraged him to think about rhythm in a new way." Bartók would make an appearance on Emerson, Lake and Palmer's first album in the opening track, "The Barbarian," with a folk effect borrowing liberally from Bartók's solo piano work "Allegro Barbaro."

The mythopoeia tradition, popularized by J. R. R. Tolkien through using the term as the title of a poem, later came to describe a modern form of mythology, one that utilizes tropes from ancient mythology to craft contemporary stories. Progressive rock shares in this literary tradition by firing myth in a furnace of modern—sometimes avant-garde—music. The court of the mysterious Crimson King could easily be a location in Middle Earth, but it transcends it through rock's uncanny ability to give even the most fantastical ideas a sense of realness. This is the occult's greatest impact on rock and roll. Over time, by incorporating mystical and magical elements into its music and presentation, rock created a mythos around itself suggesting it was somehow heir to secret wisdom. Sometimes malevolent, sometimes mystical, this special perception of things unseen would drive both its fans and detractors to obsess over possible esoteric meanings.

Like musique concrète and the spirit of music's future it hoped to help shape, listening to rock became a deeply subjective experience. Sometimes it was believed the musicians themselves were just vessels, often unaware they were being used to telegraph designs beyond themselves. The fan at the Roger Dean art opening would not accept that the artist was just grooving off the grand narratives sculpted by his clients. If Dean didn't intend to convey any spiritual riddles, then maybe the bands didn't, either. But this would be shortsighted and obtuse. The only logical conclusion was they were simply conduits, unaware they were being manipulated by the gods. The right formula of mythic world building, extensive use of Moogs, and Roger Dean's artwork could send a band into the stratosphere.