They deliberately chose very low specs. A lot of the higher end gamers are complaining that they can't see how the game will look good with those specs, but they're catering to the TBS market, not the FPS market, so they weren't too concerned about that.
Though in truth, with a system like that, you will probably be just barely able to play the game. The AI will take an inordinately long time taking its turns, graphics will load very slowly when changing screens, it might be a touch hard to tell what's going on in combat with all the graphics set to minimum, etc. I played Civ3 on a Celeron 400 for a while before getting my current system, and there was a reason why I refused to play on anything larger than Standard maps, and preferred smaller ones.
To get a really playable game you will almost certainly need a substantially better system. Of course I doubt that's news to anyone, but I thought I'd mention it.