Heavy metal's Big Four -- Metallica, Slayer, Megadeth and Anthrax -- will ride together in 2010. In Europe, at least.

After weeks of rumors, the four bands have announced they'll take part in the traveling Sonisphere festival, starting June 16 at Bemowo Airport in Warsaw, Poland and continuing June 19 in Prague, Czech Republic. More Big Four Sonisphere performances are expected to be announced in the coming weeks; the festival's web site (sonisphere.com) currently lists 15 dates, including two-night stands in Sofia, Bulgaria, Bucharest, Romania, Istanbul, Turkey, and Knebworth, U.K.

There's no word on U.S. dates for the Big Four. Slayer, who co-headlined the 2009 Mayhem Tour, and Megadeth are teaming up for a 26-date American Carnage tour of North America that kicks off Jan. 18 in Seattle. Metallica toured extensively in 2009; it was No. 11 overall on the Billboard year-end Boxscore, playing to 1,120,917 fans and grossing more than $76.6 million in 66 concerts.

In a statement, announcing the Sonisphere shows, Metallica drummer Lars Ulrich says that, "Who would have thought that more than 25 years after its inception, thrash metal's big 4 would not only still be around and more popular than ever, but will now play together for the first time...what a mindfuck! Bring it on!" Slayer's Kerry King adds that, "It's about fucking time this happened, and about time the fans finally get what they want. This is fucking awesome."

Megadeth leader Dave Mustaine notes that the Big Four shows are "a 'once-in-a-lifetime' opportunity for heavy metal 'fans' to see the four greatest heavy metal 'bands' in American history back together on one stage. If there are any heads left at the end of this Festival that haven't banged, they don't belong there."

Anthrax's Scott Ian, meanwhile, says the tour ends "26 years of expectation," adding that "I believe not only will we live up to the expectations, we will shatter them!! No other four bands as influential as the four of us have ever done this. Imagine if the Beatles, Stones, the Who and Zeppelin had done shows? Or Sabbath, Priest, Maiden, Motorhead?...That's how big I feel this is."

Ticket information for the announced shows is available at the Sonisphere web site.