The rise and rise of Metallica into one of the major forces in rock has unfolded over the decades like a brilliantly executed surprise attack. Consider where they began: as a SoCal quartet obsessed with the loudest, fastest, darkest heavy metal imaginable in 1981, clawing and scratching for gigs while the Sunset Strip was awash with longhaired boys in lipstick and spandex.

Metallica played thrash, not pop, then fled to San Francisco and thrived.

They also reflected a rare kind of evolutionary imperative, rising forcefully from the original thrash underground they shared with Slayer, Megadeth and Anthrax, to arenas and stadiums, then shifted gears just enough in the '90s to vanquish the alternative nation. Metallica elbowed their way onto the KROQ airwaves and headlined Lollapalooza. Now comes an invasion on the hallowed site of Coachella itself.

Far bigger than a simple stadium show, Metallica will bring together the preeminent originators of thrash metal on Saturday for a daylong “Big Four” fest at the Empire Polo Field in Indio, just a week after Coachella's remnants are swept away.

It follows a Big Four tour of Metallica, Slayer, Megadeth and Anthrax last year in Europe, but the hugeness of bringing these four horsemen of thrash together for the first time in the U.S. should not be lost on the fans who will transform the site into a massive version of the cult short film Heavy Metal Parking Lot.

A crowd of 50,000 is expected. “The mainstream ended up embracing us,” Metallica drummer Lars Ulrich told me the day the show was announced in January. “That obviously doesn't suck.”

Birthed largely in Southern California, thrash was a collision of British heavy metal and hard-core punk, a revolutionary noise that was too fast and even a little scary in the right hands. Unlike other products of the '80s, the genre has never faded into nostalgia and obscurity — instead, it continues to renew itself with generation after generation of disaffected teens in black T-shirts and pierced flesh.

“It hasn't strayed away from its attitude, that punk root that it's attached to,” says Slayer drummer Dave Lombardo. “The music isn't fake. The people who are associated with thrash metal, they like their music. It's stayed true and people respect that.”

Following the founding fathers, a number of later acts emerged playing even faster, but it was a pointless exercise, more macho than musical. Meanwhile, Metallica became one of the biggest rock bands in the world, filling stadiums as easily as U2 or the Rolling Stones, and got themselves voted into the Rock and Roll Hall of Fame in 2009, where frontman James Hetfield humbly described his quartet as “somewhat of a heavy band.”

The other three bands on this weekend's bill did all right in the money-and-fame game as well. Slayer earned their first gold record in 1986, with the Rick Rubin–produced thrash-horror milestone Reign in Blood. Hitting platinum that same year were Megadeth, a jazzier thrash act formed by guitar-shredder Dave Mustaine after he was fired from the original lineup of Metallica. New York–based Anthrax became stars of MTV, collaborating with Public Enemy on the influential 1991 metal-rap mash-up “Bring the Noise.” The once-preposterous idea of thrash reaching world domination was only a joke until it wasn't.

“There's a lot of intelligence in the music, in the lyrics, in the business of all four bands,” says Anthrax guitarist Scott Ian. “Maybe we don't look like the smartest dudes in the world, but every one of these four bands has some really smart people in it — creatively, professionally. We all had a very strong vision.”

Why, a neophyte might ask, are these particular four bands universally acknowledged as “The Big Four”? What makes precisely these longhairs (and shaved heads) so damn big? Surely other bands of their generation were equally fast and furious, just as committed to darkness and gloom. Their fellow travelers in Testament and Exodus and elsewhere also carried the uncouth thrash flag in the awkward days of hair metal.

What separates the Big Four from their brethren is the reality that Anthrax, Megadeth, Metallica and Slayer were not only originators of the thrash sound, but each transcended their own genre. Their names are known to those who have never heard them. Bad reputations precede them.

The idea of a Slayer/Megadeth concert remains a vaguely threatening concept to the uninitiated. Last summer, a small crowd of Christian protesters stood vigil outside their show at the Long Beach Arena, still fighting a culture war that ended long ago (maybe when Ozzy Osbourne moved next door to a chummy Pat Boone in Bel-Air). Slayer frontman Tom Araya was raised a traditional Catholic, and Megadeth's Dave Mustaine and David Ellefson are openly born-again Christians. “It just shows that [the protesters] don't know me,” Mustaine says. “If you really want to preach the Gospel to people, you have to do it with your deeds and not your words.”

Mustaine stopped drinking, tries not to swear onstage and has happily accepted the warming of relations between himself and Metallica. The outspoken red-haired guitarist was famously ejected in 1983 during a road trip to New York to make the debut album, and sent home on a Greyhound bus. (His immediate replacement was Kirk Hammett.) The insults were hurled back and forth for decades after, sometimes in fun, sometimes not.

The warfare between the metal camps is long behind them, evaporating completely during a Big Four concert last year in Sofia, Bulgaria, when members of all the bands jammed through Diamond Head's “Am I Evil?” together onstage.

“We've gotten beyond all the tension of the past,” Mustaine insists. “When you're looking at an audience of 100,000 several times a week, it has a way of making you forget about the petty stuff. Honestly, it's like fly shit on a dance floor.”

The Big Four concert featuring Metallica, Slayer, Megadeth and Anthrax happens Sat., April 23, at the Empire Polo Field in Indio (aka the Coachella Music Festival site).

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