In 1938, a struggling science-fiction writer named T.H. White abandoned the postapocalyptic tone and setting of his previous novels and reached back into the past. He grabbed a copy of Thomas Malory’s 15th-century text Le morte d’ Arthur and wrote The Sword in the Stone, a story detailing King Arthur’s coming of age (including his tutelage by the magician Merlyn) and spiked it with references to Freudian psychology for modern resonance. By 1958, White had published an entire series of Malory-inspired novels, collected together under the epic title of The Once and Future King. The book, which found its way onto best-seller lists and high school curricula, begins with a Latin quotation proclaiming Hic iacet Arthurus, rex quondam, rexque futurus, which means, "Here lies Arthur, king once and king to be."

It’s an inscription suggesting circularity and rites of succession, a tale worth telling over and over on down the generations. There’s a fine line between archetype and cliché, however, and the question of whether we need one more version of the boy-meets-sword saga — even one featuring a cameo from the not-quite-knighted David Beckham — remains very much open. The word on Guy Ritchie’s new, CGI-infested King Arthur: The Legend of the Sword is it’s vulgar, generic, and redundant; if chivalry isn’t dead, it’s on life support. At this point, everybody from Walt Disney to Robert Bresson to Monty Python has already taken their shot at Camelot. You come at the king, you best not miss.

Of all the film adaptations that have wrestled with the Arthurian legend, the one that comes closest to capturing its grandeur is John Boorman’s Excalibur (1981), a mad, magnificent movie that belongs on any responsible list of modern cult classics. It’s also easily the most ambitious and bizarre entry in a cycle of elaborate, expensive fantasy pictures commissioned in the early ’80s in the aftermath of Star Wars, a list that also includes Dragonslayer, Legend, and Conan the Barbarian. The industry’s thinking was that George Lucas’s blockbuster was basically just the Knights of the Round Table in Space, so why not swap out the lightsabers for broadswords and give the people what they really wanted?

Boorman was perhaps the most talented and eccentric of the new guard of British filmmakers that sprung up in the 1960s. He was quickly recruited to Hollywood for the magnificent pop-art hitman thriller Point Blank before scoring multiple Oscar nominations for Deliverance. Nobody made weirder, more audacious genre movies in the 1970s than Boorman: Both the science-fiction satire Zardoz, featuring a beefy, diaper-wearing Sean Connery as the last sexually potent man on earth, and the critically reviled Exorcist II: The Heretic were deluxe, delirious, all-out follies that left audiences wondering what the hell they had just seen.

Boorman’s dream project was a movie version of Lord of the Rings, and he had Tolkien on the brain when preparing the script for Excalibur. "I’m trying to suggest a kind of Middle Earth," he told an interviewer before the film’s release. "It’s a contiguous world; it’s like ours, but different."

The only way to describe Boorman’s imagery in Excalibur is otherworldly: Its visual magic was conjured up by cinematographer Alex Thomson with an array of dazzling angles and lighting cues that are the equal of anything in Blade Runner. (He was rewarded with an Oscar nomination for his work.) A prologue describing a nighttime clash of armies, all clad in terrifying animal-mask helmets, is ringed by smoke beneath blood-red torch lights before the the color scheme shifts to a blinding array of greens. The film was shot on location in Ireland, and the color palette evokes the title of another one of Boorman’s films: The Emerald Forest.

The landscape in Excalibur feels almost impossibly fertile, which fits Boorman’s conception of Arthur’s rise, fall, and redemption as a kind of national creation myth. The opening scenes are fixated on baby-making, as the crafty wizard Merlin (Niccol Williamson) uses his magic to transform reigning monarch Uther Pendragon (Gabriel Byrne) into a double of his rival Gorlois, the Duke of Cornwall (Corin Redgrave) so that he can impregnate the latter’s wife with the child who will grow up to be Arthur. (Boorman cast his daughter Katrine as the seduced duchess, who is naked while Uther grinds away on top of her in full battle regalia; as gestures of fatherly support go, this one is a bit ambiguous.)

Later on, long after retrieving his royal birthright in the form of Excalibur and growing up into a benevolent king, Arthur (Nigel Terry) will end up on the other side of the sort of mistaken-identity sex that led to his conception, succumbing to the charms of his evil-sorceress half-sister Morgana (Helen Mirren). With the incest, adultery, and relentlessly brutal, R-rated violence, Excalibur has the lurid atmosphere of an exploitation movie. filtered through the Shakespearean pedigree of its cast (including a pre–Picard Patrick Stewart). At times, the whole thing feels perilously close to Monty Python and the Holy Grail, minus the wicked sense of self-awareness. Boorman isn’t just staging an adventure epic: He’s mounting a full-scale allegory about the rise and fall of Western civilization.

"The future has taken root in the present," intones Merlin at one point, echoing White’s themes of recurrence and repetition. All the heavy philosophizing can be hard to take. The shots of Arthur, Lancelot, et. al staggering around the woods inside their rusty suits of armor are like emblems of the film’s exhausting, severe approach. The Arthur myth is all about purity, though, and Boorman’s belief in the material sends it soaring past silliness. The best moments, like the sudden revelation of a massive army concealed by fog, or a scene where a hero pulls his impaled body painfully along the shaft of his rival’s spear to deliver a death blow, are unforgettable. (Zack Snyder, no stranger himself to over-the-top mythmaking, quoted the latter choreography at the end of Batman v. Superman, and also proudly displayed the film’s poster outside the movie theater where Bruce Wayne’s parents are murdered.)

"Are you just a dream, Merlin?" Arthur queries his mentor at one point. "A dream to some," the wizard whispers, before adding ominously "a nightmare to others." Excalibur isn’t for everybody, but for kids who grew up reading T.H. White and wondering what all that magic might actually look like, it’s the stuff that dreams are made of.