In a 3-city-game you're not allowed to build more than 3 cities. This is enforced by a ruleset that disables settlers, but allowes a new unit "emigrant" to be build. The emigrant is nearly identical to the settler, but it can't found new cities. You can still use it as (expensive) worker or to move population from one city to another. Without that rule, you cannot AI a player when he disconnects, because the AI will start to build new cities. Some players think, you should be allowed to build a new city, when you lose one, but that rule is inacurate, and might leed to unfair tactics when two players work together. Plus, if you lose a city it is too late to found a new one anyway, so i dont see practical use for a rule like that, and it prevents the usage of AI. Ruleset to enforce 3-City-G