In 1973, legendary British DJ John Peel had some warm words for a new album.

"In 20 years' time," he wrote, "I'm ready to bet you a few shillings that Yes and ELP will have vanished from the memory of all but the most stubborn and that the Gary Glitters and Sweets of no lasting value will be regarded as representing the true sound of the 1970s. Having said that, I'm going to tell you about a new recording of such strength, energy, and real beauty that to me it represents the first breakthrough into history that any musician regarded primarily as a rock musician has made."

The album: Mike Oldfield's Tubular Bells, one of the weirdest and hugest commercial hits of the progressive rock era. Peel's review captured prog-rock's vast ambition. It wasn't just rock, it was serious music played by virtuoso performers incorporating structures (and, not infrequently, melodies) from classical music, the improvisatory flair of latter-day jazz, and the studio experimentation associated with avant-garde artists like Karlheinz Stockhausen and John Cage.

All of that was wrapped into concept-album pretensions that were alternately taken with extreme seriousness (as in Genesis) or with no seriousness at all (as in Jethro Tull). As music writer David Weigel observes in his new book The Show That Never Ends, the story of prog rock involves a puzzle. In its '70s heyday, prog rock was phenomenally popular and critically acclaimed, but once it crashed, it never really rose again.

Disco lives on as a narrative of queer empowerment and undeniable beats, and punk rock is revered anew by every generation — but what about Tubular Bells? Sure, Pink Floyd's Dark Side of the Moon remains a touchstone. It landed in the top five of The Current's 893 Essential Albums listener poll. Outside of Pink Floyd, though, prog rock is absent from the top 100 albums. (Some diehards think that Pink Floyd aren't true prog because they're insufficiently dedicated to instrumental virtuosity, which actually might explain a lot about their enduring popularity.)

Just because people aren't dropping a lot of needles on In the Court of the Crimson King these days, though, doesn't mean that prog is dead. Artists like Radiohead (despite their vehement disavowals), St. Vincent, Frank Ocean, Tame Impala, and many more are clearly part of prog rock's legacy.

Weigel's book starts in 1840, with a description of the flamboyant performances by the pianist and composer Franz Liszt. Over a century later Liszt would be the subject of a 1975 film, Lisztomania, with a soundtrack by leading prog artist Rick Wakeman. Weigel argues that Liszt embodied much of the spirit of what came to be known as progressive rock: music composed with discipline but performed with a showy flair that enraptured Liszt's audiences.

Fast-forward to the 1960s, when musically sophisticated young musicians in Britain sought to combine classical grandeur with the rock-and-roll pulse of their generation. If rock started as a melding of black R&B and rural white country music, suggests Weigel's history, prog rock was the creature of middle-class white musicians who were less interested in rock as rebellion than they were in its possibilities as a color in a broader musical palette. ("We weren't on acid," remembered Genesis guitarist Steve Hackett, "we were on beer and wine and Earl Grey.")

By the mid-1960s, that impulse spurred the creation of bands like Soft Machine and the Moody Blues, whose landmark album Days of Future Passed (1967) was commissioned by Decca as a rock-orchestra hybrid that would fully demonstrate the possibilities of its new stereo sound system.

That same year, prog had a commercial breakthrough with Procol Harum's signature hit "A Whiter Shade of Pale." For the song's hook, Gary Brooker adapted a melody from J.S. Bach's Air on a G String. The Hammond organ, so familiar to rock listeners, was being reconnected with the instrument's classical genesis.

The core of Weigel's book follows prog from there into the late '70s. Generously filled with quotes from contemporary media coverage, the book is long on facts and relatively short on analysis. Social context also gets short shrift — we learn about inter-band spats and the origins of albums, but we don't learn much about who prog fans were, and what the music did for them. There's an Old-Testament feel to much of the book: the Nice begat ELP, and ELP begat Asia, and so on.

A New Yorker review by Kelefa Sanneh provides the kind of helpful insight that's hard to dig out of Weigel's book itself. Prog, notes Sanneh, was an unapologetically — even stereotypically — British art form. Unlike the Beatles or the Stones, prog musicians weren't remotely trying to sound like Chuck Berry.

In a thoughtful 2009 autobiography, Bill Bruford, a drummer who was central to the development of prog rock, noted that many of the music's pioneers were "nice middle-class English boys," singing songs that were "self-consciously British." Genesis, for instance, was formed at Charterhouse, a venerable boarding school in Surrey; the band's album Selling England by the Pound was an arch and whimsical meditation on national identity. Bruford pointed out that even Pink Floyd, known for free-form jam sessions and, later, cosmic rock epics, found time to record songs like "Grantchester Meadows," a gentle ode to the East Anglian countryside.

One thing prog did, certainly, was to provide a live experience. Bands like Genesis often performed entire albums live — sometimes with associated stage shows — but even when they didn't, a lot of prog song-suites were so long that they were essentially miniature albums onto themselves. For the right kind of listener, a prog concert created the kind of experience a listener today might find at a jam-band show or an EDM performance. The music just kept coming, and coming, and coming. (As Sanneh notes, a malfunction involving the members of Yes emerging from giant onstage pods inspired the "Rock 'n' Roll Creation" scene in This is Spinal Tap.)

There was a lot of turnover in prog bands — the Wikipedia editors who maintain those detailed band-membership timelines are doing yeoman's work — and Weigel follows artists like Keith Emerson and Robert Fripp from one band to another as they seek constructive collaborations and, if possible, commercial success. Fripp comes across as perhaps the definitive true prog believer: the one guy who never sold out, going from King Crimson to collaborations with the likes of David Bowie (Heroes) and Talking Heads (Fear of Music) and back again.

Did I say "sell out"? Well, you might prefer a more generous term — I would, myself — for the fact that some of prog's most ambitious artists became some of the 1980s' biggest hitmakers. Phil Collins stepped forward and turned Genesis into Top 40 regulars, while former frontman Peter Gabriel trimmed his former band's excesses and built a wildly successful solo career on a more minimal sound that emphasized feeling and tone over instrumental pyrotechnics. Yes, in their umpteenth configuration, lured singer Jon Anderson back with the promise of a commercial hit and immediately went to number one with "Owner of a Lonely Heart."

Then, of course, there was the prog "supergroup" Asia, which had a smash with "Heat of the Moment" and deeply depressed the critics who had loved its members' work in Yes, King Crimson, and ELP. "The sound of Asia is as homogeneous and inoffensive as Cream of Wheat," wrote one critic cited by Weigel. "Asia is nothing less than a turning-in upon itself of late-70s commercial cynicism, spawned by the very 'progressive' musicians that initiated rock's backslide."

You can't climb up that hill again, and after its turn-of-the-decade crash (which, Weigel notes, was accelerated by a slump in overall record sales that made cash-strapped labels less enthusiastic about hiring orchestras to back rock bands), prog was never really the same.

Though Weigel's priority isn't to dig out the juiciest stories from prog history, he does have a few good anecdotes. I learned, for example, that "Nights in White Satin" was inspired by Justin Hayward's frustrations with a set of satin sheets his girlfriend gave to him. Have you ever tried sleeping on satin with a beard? Apparently it's not pleasant.

Weigel also recounts an explosive backstage fight between Emerson and Carl Palmer after Emerson called for a cover of B. Bumble and the Stingers' "Nut Rocker" that Palmer thought only served to showcase Emerson's keyboard skills and make the rest of Emerson, Lake & Palmer look ridiculous. A wine bottle was smashed, voices were raised.

Prog famously relied on jury-rigged instruments like the Mellotron — a tape-keyboard hybrid that effectively served as an analog sampler. For a period, Yes toured with a keyboard tech who spent the entire show lying beneath Rick Wakeman's organ, both to fix the inevitable glitches and to "continually hand me my alcoholic beverages," Wakeman explained.

The Show That Never Ends is useful both as a history and as a reminder of just how extreme prog was at its proggiest. Consider this sentence about the band FM. "The group was founded by vocalist and multi-instrumentalist Cameron Hawkins, who was joined by drummer Martin Deller and violin and mandolin player Nash the Slash, who performed while wrapped up in bandages like a mummy." Far out.

For more prog awesomeness, tune in to Teenage Kicks this coming Saturday morning (8-10 a.m.) to hear Jim McGuinn's interview with Tony Levin of King Crimson.