As you know, the Byzantine Empire is the theme of Crusader Kings II: Legacy of Rome and patch 1.07, and an integral part of the Empire was of course the Orthodox faith. So, today I'll talk about a feature we planned to put in the DLC, but later decided to make a free part of patch 1.07; Autocephalous Patriarchs and the Pentarchy.
The main difference between Orthodox Christianity and Catholicism is probably the lack of a single leader (although the Ecumenical Patriarch of Constantinople is nominally the first among equals.) Instead, there are a number of practically autonomous Patriarchs, though they remain in communion with the rest of the Orthodox Church. This is called autocephaly, and we now represent this in the game by making the Court Chaplain in Orthodox kingdoms a Patriarch who is the religious head of everyone in the kingdom. He has power over excommunication and divorce over all characters in his jurisdiction, though only the Ecumenical Patriarch can grant invasions. Autocephalous Patriarchs have to be bishops (rule a temple Holding), preventing them from marrying or inheriting titles.
However, this is not all; we are also adding another concept called the Pentarchy. These are the five original heads of pre-schism Christianity; the bishops of Rome, Constantinople, Alexandria, Antioch and Jerusalem. If there is an Orthodox bishop in one of these Holdings, he will be considered a Pentarch, and will act like an autocephalous Patriarch over his entire traditional see (Orthodox kingdoms within such an area will not have their own Patriarchs.) Each reigning Pentarch will strengthen the authority of the entire Orthodox faith. Incidentally, this mechanic also has bearing on some key Decisions in Legacy of Rome (more on that in the next dev diary.)
As an added bonus, we are making the other forms of Oriental Christianity a bit more interesting. There is now a religion called Miaphysite, which includes the Coptic Orthodox Church and the Armenian Apostolic Church. In game terms, it's another version of Orthodoxy, with its head in Alexandria instead of Constantinople. It has the same mechanics with autocephalous Patriarchs and the Pentarchy as Orthodox Christianity, but is not considered a heresy by Catholics and Orthodox Christians. The Monophysite heresy is now a heresy of the Miaphysite Church. Lastly, most Orthodox heresies now also work like Orthodoxy itself, and we've added the Nestorian and Monothelite heresies.
(Notice the African faces - they're another DLC in progress.)
The religious system with the new Orthodox features is of course fully moddable, though you cannot combine investiture and antipopes with the Pentarchy mechanic.
That's all for now. The next dev diary will be the last, and will deal with the unique decisions, events and mechanics in the Legacy of Rome DLC.