'In all modesty, this is the best metal show of all time," Anthrax guitarist Scott Ian says of the Big 4, the bash that Metallica, Slayer, Megadeth and Ian's band threw in Indio, California, on April 23rd. Thrash metal's titans have played together before – they toured Europe last year – but their U.S. debut, peaking with Metallica's triumphant closing set in front of 50,000 head-bangers, still felt historic.
The party in the parking lot started hours before the music, with metalheads in sleeveless pentagram T-shirts drinking, grilling and spraying sunscreen on tattooed skulls. As Anthrax began their sweaty 4 p.m. set with 1987's "Caught in a Mosh," fans rushed to the stage, pumping fists and throwing up devil signs. "The emotion coming off the crowd was unlike any I'd felt in the U.S.," says Ian. Megadeth followed with another intense performance, tearing through cuts like 1986's "Peace Sells." Frontman Dave Mustaine's red mane swung in his face as he shredded on a golden Flying V, unfazed by technical problems. "I held my anger in for the whole set," says Mustaine. "But at the end, I kicked my guitar into pieces."
The unparalleled aggression of Slayer's set inspired the day's most brutal mosh pits. In a moving moment, guitarist Jeff Hanneman – sidelined this year by a flesh-eating bacterial condition that withered his right arm – made a surprise appearance, defiantly displaying his scarred limb while he played on "South of Heaven" and "Angel of Death." "It was so fucking great being onstage again," Hanneman says. "I could see the look in the kids' eyes when I got up there."
Ultimately, the night belonged to Metallica. Taking the stage around 8:30, the band ripped into 1984's "Creeping Death." Frontman James Het-field led the crowd in a "Die! Die!" chant – the first of many epic singalongs in a career-spanning two-and-a-half-hour set. During "Enter Sandman," fans started a roaring bonfire in the mosh pit. Later, Hetfield called the other bands onstage for a raucous cover of U.K. metal pioneers Diamond Head's "Am I Evil." The crowd erupted when Mustaine – who was unceremoniously kicked out of Metallica in 1983 – was the first to appear. "That morning, James sent me a text saying, 'Are you ready to kick ass?'" says Mustaine. "We're buddies again."
At a photo shoot that evening, Metallica guitarist Kirk Hammett hugged Slayer's Kerry King, and Metallica drummer Lars Ulrich good-naturedly teased his Megadeth counterpart, Shawn Drover, about his perfect hair. "The camaraderie is real," Ulrich says. "A segment of the metal community would rather have us still feuding, but there's nothing to be competitive about now." While Metallica are discussing a possible new album and tour, their immediate priority is the Big 4, who will play Yankee Stadium in September. "This thing should play more places," says Ulrich. "Still, I don't think it will turn into a 40-date arena tour. That would make it less special."
This story is from the May 26th, 2011 issue of Rolling Stone.