Indeed, religion plays a much larger role throughout the game. Special religious emissaries can be built and deployed to provinces to encourage the growth of a particular religion. A predominantly Orthodox province occupied by a Muslim power is more likely to revolt - sending an Orthodox priest can make a rebellion more likely as it encourages the growth of the Orthodox religion. Other diplomatic unit types include emissaries, princesses, and assassins. Emissaries are general diplomats, and can be used to spy, counterspy and bribe enemy generals into defection. Princesses can be uses as spies, but their primary use is cementing alliances through marriage. They can also be used to reward your generals and tie their loyalties to the royal house. Assassins, well, they kill people, and can be used to counter enemy assassins. One interesting group of units are the Inquisitors. Their primary function is to raise the zeal of the population of whatever province they're in. This is a delicate business, however, because leaving Inquisitors in a province too long results in them going a bit Monty Python, and attempting to burn everyone at the stake, at which point the zeal of the province falls through the floor. Inquisitors have other useful functions though - they can be used to accuse any catholic leader unit of heresy. This includes enemy generals, kings or even the Pope, with the rank of the Inquisitor and the piety level of the accused being used to decide the outcome.

The three main faction groups each face different problems and inherit certain advantages. Catholics can call crusades, which given the right conditions can snowball into massive offensive armies once they arrive at their destination. Catholics alone also have access to the Inquisitor unit. Catholic factions, however, must at all times deal with the royal pain in the arse that is the Pope (unless you eliminate him). The Pope essentially enjoys poking his nose into everybody's business, and becomes especially uppity whenever Catholic factions attack each other. This situation usually results in somebody being excommunicated, and the Pope calling on other Catholic factions to attack the offending party. Muslim factions are capable of ordering a "Jihad". This is somewhat different from a crusade, in that it can only be used defensively to gain back a lost province. It is not, therefore, as useful as a crusade, but then Muslim factions don't have to worry about the Pope's meddling. Orthodox factions do not have an equivalent ability, but they do have the advantage that their provinces are less zealous than either of the other religions, and so they are largely immune to the effects of a late game crusade, as the crusade just dies off when it leaves catholic regions. There are several factions of each religion available for play, and each provides a different playing experience. Each faction has a specialised unit available only to itself - the English can produce longbowmen, for instance. The major difference, however, to how each faction plays results from two things. One is its starting position, and the second is the era you begin the game. You can choose to begin in the early, middle or high medieval period, and each faction's position is quite different in each time period. The French, for example, find themselves in a very difficult position in the early game, with the English occupying large parts of France and the Germans pressing from the east. Choosing to play in a different era will result in a different set of starting circumstances. These differences serve as providing different challenges outside of the main difficulty level of the game.