Inciting religious revolt/ converting the people to your cause

[Furious Mental]

On an ERE campaign I played, I found Colchis to be a very troublesome city to hold on to. The problem was not that my army was weak, it was more than capable of fending off the Sassanids (even had some mercenary elephants). The problem was that public order would often drop to terrible levels in only one or two turns (only caused alot of rioting, no rebellions, fortunately). Eventually I realised that this was because Sassanid characters with pro-conversion traits and retinues were sitting in my province converting the population to Zoroastrianism. I am not sure if the AI was actually intending to do this, but it certainly had that effect. Fortunately because it's a small province it was fairly easy to deal with, but in large provinces it could be seriously troublesome because during the time it would take to find and fight off the interloping army the city could rebel. I tried it against the AI too, and managed to cause a couple of provinces to go rebel. However, it's mostly useful for preparing a province for takeover by your army. Might be a totally obvious tactic and I'm just dumb for only having stumbled upon it, but if you have surplus generals they can make occupations alot easier by helping to convert the population before you capture a city. I believe it can also be done with diplomats, if they have religious traits.

[Drusus Magnus]

Haven't seen the AI do that in my campaign. Colchis always revolts to me. Although, I believe, the Sassanids do start with a character which, with retinues and traits combined, has about +40% conversion for Zoroastrianism. Send assassins/armies. Or have a christian teacher stay in the province, I think that's about all you can do.

[Trithemius]

You can use sunny Colchis as your "retirement home" too.

If you have a place where an alien religion seems to keep increasing, rather than reducing, you can send all your "retired" family members and generals there. I like to recycle my commanders quite a lot, to avoid serious loyalty problems (and once you get some good ancilliaries its not too bad to lose the general's command rating for a short time) and I like to dump them all somewhere out of the way. If most of the them are Christian you can have them collect anchoresses (who are less useful than anchorites in my opinion), the unrest-causing relics, and spare bishops (I have a whole sack of bishops, it seems!) and ship them off to Colchis. This should keep the conversion in check, until you get a chance to clear the Sassanids off the map and establish proper religion in their former provinces.

[Tyrac]

Diplomats have religion. You can quite literally swamp a region with your diplomats and alter its religious make up tremendously. It is a cheap and easy way to counter the AI doing it to you and to prep regions for religious revolt or conquest and conversion.

[Tyrac]

Diplomats have religion. You can quite literally swamp a region with your diplomats and alter its religious make up tremendously. It is a cheap and easy way to counter the AI doing it to you and to prep regions for religious revolt or conquest and conversion.

Actually I should preface that and say SOME diplomats have religion. I just made one that had none. Was rather odd.

[Conqueror]

I get those "faithless" diplomats most of the time. Even if I train them in cities with big temples it's still uncommon for them to have religious traits.