Hard to believe it now, but Metallica weren't always the undisputed heavyweights of heavy metal. There was a time in the freewheeling '80s when that title was still up for grabs, and the so-called Big 4 (Metallica, Megadeth, Anthrax and Slayer) were all reaching for the crown.

That time is obviously long gone, and the now-friendly Big 4 just staged a concert together at the new Yankee Stadium in New York (read our review and see a photo gallery of the gig here). Rolling Stone got the chance to sit down with the bands and discuss the differences between now and then, as external conflict evolved into an internal drive for each band to better itself.

As Metallica's Lars Ulrich said: "A lot of things have changed over the years. When you get out of the sandbox and grow up, you stop worrying so much about what everyone else is doing ... To me, the competition is now internal. That's the biggest difference from 20 years ago."

"I think we were friendly rivals," says Slayer's Kerry King. "I would always want to get Metallica's record as soon as it hit. Megadeth's record. Anthrax's record. To see what they are doing, you know? Kinda like egg you on, pushing you to be better."

Hear more of what Ulrich, King, Slayer's Tom Araya and others had to say about the rivalry in this video: