Culture is definitely one of the few key points in Civ 3. By building Libraries, Temples and other educational and religous buildings you gain culture points that are consistently added to your "culture bar" that extends your territory and ability to work that territory when filled. The target amount of culture points rises exponentially by 10. The ability to extend the amount of land a city can work is very impressive and a very big plus. I'm not sure but i think that when your territory extends into an enemy city you can take it over. This is probably the coolest added gameplay feture from Civ 2.