Well, the Bible says that you shall rest on the seventh day of the week, which in certain religions is known as Sabbath or Shabbat or whatever, which as we all

Well, the Bible says that you shall rest on the seventh day of the week, which in certain religions is known as Sabbath or Shabbat or whatever, which as we all know maps to Saturday. Without having really done the research, I've been ascribing the US calendar idiosyncrasy to religious influences... and really, that's what Europe does as well, they just picked a different mapping. So now when we rest, both the Jews and the Christians get their favorite day off and yay, we have a two-day weekend.