The last time the Big Four of thrash got together for one show – those being Metallica, Slayer, Megadeth and Anthrax – was in 2011 at Yankee Stadium. Slayer is currently on their farewell tour, so if there's going to be more one of these shows, now would probably be the time. Megadeth frontman Dave Mustaine says he hopes there will be one more in the future, but there's been no rumors that there's even plans for one.
The closest thing fans will get right now is Slayer, Megadeth and Anthrax all sharing the stage at the Santiago Gets Louder festival on October 6 in Santiago, Chile. The three will be joined by a band called Pentagram from Chile, which is not the Bobby Liebling one.
It's worth noting Metallica will not be on tour during this time. So maybe they'll show up?
