You can't really discuss Civ's combat system, though, without calling to mind those infamous situations where some Stone Age unit manages to defeat a modern tank, or even a battleship. Though Firaxis swears that should only happen about 1 percent of the time, that's still too high for fans. So Civ IV throws out the old attack and defense ratings and introduces a new power rating. "In Civ III, every [regular] unit had three hit points, basically. The issue there was a spearman could beat a tank because it just had to get lucky three times," Johnson said. "In Civ IV, the amount of damage a unit does to another unit is now out of a scale of 100, even though that's more or less hidden from the user. The amount of damage a unit does is relative to its different strengths. So now when a spearman attacks a tank, he may hit three times, but that's only going to take off a quarter of the tank's hit points. Meanwhile, a tank hitting a spearman only has to hit him once or twice, and he's gone entirely."