It's the first Thursday of a new month, and the stars just happen to be exactly right for a new entry in the Crusader Kings II developer diary! God willing, it will be an enlightening one. Yes, my friends, it is time to get serious and talk about religion, and, being a game about medieval times, religion obviously plays a huge part.
There are three groups of religions in CKII: Christian, Muslim and Pagan. Each group encompasses the main religions (e.g. Catholic and Orthodox) and their heresies (Waldensian, Bogomilist, etc.) Now, the specific religions have certain characteristics that set them apart from each other. For example, Catholicism has an independent chief pontiff (the Pope) who can excommunicate people and call for crusades. He can also, on rare occasions, grant a divorce or a special Casus Belli. Rulers can request excommunications, divorce or an invasion casus belli from the Pope, but it will cost them a lot of Piety, and requires that the Pope hold them in high regard.
Perhaps the most central feature of the Catholic Church, however, is the investiture of bishops. As you probably recall, fiefdoms can be held by members of the clergy (the rich and juicy Temple type baronies in particular). The income from these holdings normally goes to the Pope and not the secular liege of the bishops. However, if the Prince-Bishop happens to like his liege more than the Pope, he will instead pay taxes to his liege (and allow his troop levies to be raised.) The problem is just that the clergy naturally tends to favor the Pope, which is why kings can pass a law called Crown Investiture. This allows them to appoint new bishops who are appropriately grateful and loyal. Why not just do this all the time then? Because the Pope will be most displeased with kings who have passed this law, effectively barring them from any special Papal favors. There is a way around this problem too though: antipopes. Kings with Crown Investiture and high enough Prestige can set up a Pope of their own; an Antipope. This will ensure that all of the bishops in the kingdom pay taxes to the Crown, and will allow the king to excommunicate characters within the kingdom (but not outside it), arrange divorce, etc. Moreover, characters within the kingdom are immune to excommunication by the Pope, and foreign bishops who prefer your antipope might actually pay taxes to him (and therefore to you.) Antipopes cannot call for Crusades, however.
Another downside is that the setting up - and existence of - antipopes harms the "Moral Authority" of your religion. This value represents how respected the religion is and its general hold over the faithful. When the value is low, the chief pontiff can no longer call for Crusades, heresies start to run rampant, and characters and provinces will not convert to the religion easily. It is all a trade-off, and trade-offs are the heart and soul of good gameplay.
What about the other religions then? Well, in Orthodox Christianity the chief pontiff is the Ecumenical Patriarch of Constantinople, and he is vassal to the Byzantine Emperor. There is no investiture conflict (church taxes go to the secular liege) and the Patriarch cannot call for Crusades. However, he can excommunicate characters and grant CBs and divorces. Pagans have no chief pontiff at all and lack all the special mechanics. The two Muslim religions (Shi'a and Sunni) resemble Orthodoxy, but the Caliph himself is the chief pontiff, and they can call for Jihad.
That's all for now. At some point I will talk more about heresies. Until next time!
Henrik Fåhraeus, Associate Producer and CKII Project Lead