I binged Season 1 on Netflix over the course of a week. Got antsy and ended up buying Season 2 on iTunes.
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Well, you might be able to go to the History Channel's site and watch the past episodes. I'm not sure.
I have Amazon Prime I was able to watch season 1 & 2 for free, but have to pay to see season 3. Very tempting, its an awesome show.
Tonight is the restart of Season 2. Is Amazon counting it as season 3?