The first round of the 2013 March Metal Madness' Mosh Pit region gets under way with two heavyweights ready to do battle. It's Slayer's classic 'Reign in Blood' in one corner, with Mastodon's modern masterpiece 'Remission' in the other corner, and only one of these two discs can advance to the second round in the battle to determine the best metal album of all-time.

They say your third album is often where a band truly defines itself, and if that's the case, then what a statement Slayer made in the fall of 1986 with 'Reign in Blood.' The disc by which all other Slayer albums are judged is still one of the most highly regarded metal efforts in history. 'Angel of Death' has become one of the band's biggest songs and the epic album closer, 'Raining Blood,' remains the highlight of their performances.

Mastodon, meanwhile, didn't emerge on the scene until two decades later, but they've been one of the most highly regarded bands of the 2000s, due in part to their breakout debut album, 'Remission.' This deeply personal album features tracks like 'Crusher Destroyer,' 'March of the Fire Ants,' 'Ol'e Nessie' and 'Trampled Under Hoof' that laid the groundwork for what has become one of modern metal's top acts.

So which will it be -- Slayer's 'Reign in Blood' or Mastodon's 'Remission'? Vote for your favorite album in the poll below and see who advances in the 2013 March Metal Madness Mosh Pit Region!

(This poll will end on Monday, March 18 at 11:59 PM EST. Fans are able to vote once per hour, so keep coming back to make sure your favorite album wins!)

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