What day was the world supposed to end?

The world was supposedly supposed to end December 21, 2012. Or at least thats what the Mayans thought. MORE: The Mayans didn't think the world was going to end. It was modern man who put this interpretation on it. For the Mayans it was just the end of a calendar and a start of a new one. Just like our calendar. We don't think that the world is ending each New Year.