Culture is a resource generated by cities. As culture is generated, Great People appear and enemy cities may join the player's civilization. Notifications as to the state of one's civilization's culture are given periodically by the Domestic Adviser. Cities may "flip" to another civilization if its production of culture is higher than the other civilization's. This can be prevented by building city Walls or raising the output of culture. (City walls will no longer protect cities if another civilization builds the Hollywood Wonder. Building Hollywood first protects one's walled cities.)