Piety is the principle skill for Priests/Imams. It affects their rate of religious conversion, their chances of success when denouncing Heretics/Witches, is a requirement for getting into the College of Cardinals, and for Imams is necessary for calling Jihads. Its also useful defensively when they are the target of an Inquisitor's attempt to denounce. There are a number of things you can do to increase the piety of your agent when it is created (and a couple of traits that are purely random at agent creation), and a number of other things you can do with that agent after it is born to further increase his skill.
I've included a couple of ancillaries that don't effect piety, to give the full list of ancillaries available to priests (there's only a couple that are available but do not give piety).
Piety at Birth. Buildings in city/castle and Faction Leader traits that can increase the Piety your priests are born with:
1) Natural skill: Normally 2/3 will be Blessed, 4/15 will be Divine Connection, 1/15 will be Chosen One, this is purely random (100% for +1, 33% for another +1, 20% for yet another +1 if already +2)
2) Abbey or above gives chance of Nun ancillary and also the Choir Boy ancillary (catholic or orthodox). Also, Abbey and above increase your agent limit by +2 for priests (for pagan, +2 for Temple, 3rd lvl building).
3) Cathedral or above gives a chance for Deacon ancillary (christian only), and also Strong Faith trait and Dogmatic trait
4) Mayor's Palace or above gives a chance for Royal Seminarian ancillary
5) Theologian's Guild gives 100% chance for Theologians Guild Trained trait
6) Master and Grandmaster Theologians guild give Theologian's Guild Apprentice & Journeyman, respectively
7) If you recruit your priest in a Castle (the top 3 types, with stone walls) you can get the Royal Seminarian
8) Strictly Religious. This is a new Faction Leader trait in SS 6.3. It gives +1 Piety to all of your Priests and Generals until your Faction Leader dies. The trait is mutually exclusive with Merchant Skill, Thinks of His People, Greedy Ruler and Wise Administrator. Each Faction Leader will eventually get 1 of these 5 traits.
9) Witch Hunter ancillary. 10% Chance at birth if Faction Leader has ReligiousActivity trait >1 (ie. Not merely "Religious" but at least "Dutifully Religious").
10) There's a Pagan Priest trait line available for Lithuania/Cumans/Mongols, by having any of the pagan temples built.
11) There's also a Paladin ancillary available which does NOT give Piety (gives +1 to each of Security, Purity, Violence) if your city/castle has at least a Militia Drill Square or Drill Square
12) Higher level churches that have 'Priest lvl 1' listed as an effect. I'm not convinced this does anything at all. (If anyone knows for sure the details, let me know).
13) Secretly Female, +1 Piety, purely random chance at birth, 2% (Christians only)
Actions you can take with your priest after birth to increase his Piety:
Note that you can click on any city/castle in any region where the settlement is visible and see the religion %, you do not need a spy in town for this.
Also, several of these traits require "Religionshift", this is defined as the change in the % religion, of your own religion type, from the turn each particular priest enters the region to the current turn. So, if you're Catholic and move your priest into a region that is 52% Catholic, he'll need to stay there until it is >62% Catholic to qualify for a >10 Relgionshift. The game tracks this for every priest/imam, resetting the counter for him whenever he moves to a new region (ie. it notes the ownreligion % the turn he moves into the region, and can compare this to the current ownreligion % at any time to determine religionshift).
1) Purifier trait line (Battler/Enemy/Purger of Heresy), I ALWAYS go for this first and max it out, with all my newborn priests. This is an easy way to get +3 piety on ALL of your priests in a reasonable amount of time. After they max this trait line, I usually send my priests in groups of 3 or more to newly conqured provinces that need a religion bump for unrest purposes, any provinces I own with high heresy, or I'll use them offensively against AI factions to make their cities rebel. The other actions listed below I'll go for occassionally as circumstances permit.
Trait line gives: Piety 1,2,3, with Thresholds 1,3,6. Trigger: Park in any region for >4 turns, get >10 ReligionShift, must be at least 10 turns since Heresy level <5 in that region, 85% chance per turn for +1 to threshold from 5th turn on. So, figure on average it'll take about 11 turns to max this trait line per priest, assuming you get that >10 religion shift in the first 5 turns, takes a bit longer otherwise.
So, I look for a region near where I'm building my priests that has 1) Less than 5 Heresy (this is very important as there's a 10 turn delay AFTER getting heresy below 5 before the trigger for this trait line will work, so avoid using any region with 5+ heresy when going for this trait line) 2) Has very low % of my own religion. I'll send ALL my newborn priests to this region until its religion% gets to about 80 for the turn my priests move in (since you need a >10 religion shift AFTER the priest moves in before you start getting skill, note that religion gain above 90% in a province can be very slow even if you have a lot of priests there). Once the region's % own religion gets above about 80, find the next nearest region that's suitable for skilling up this trait.
2) Missionary Trait line (Missionary/Spreader of Faith/Beacon of Faith). I never go for this, since it takes awhile to get, but its a pretty easy guaranteed way of getting an additional 3 piety and all you have to do is, well, nothing but wait if you did #1 above for the purifier trait line discussed above.
Trait line gives: Piety 1,2,3, with Thresholds 1,3,6
Trigger is: Park in Region >4 turns, ReligionShift>10, and TimeSinceReligion>95 >=10, again 85% chance per turn of +1 to threshold.
So, lets say you've been moving all your priests into a region to get Purifier trait line maxed out. To get Missionary you then simply leave them in this region until the % own religion >95 (which might have already happened while they were waiting to max Purifier), then leave them there for 10 turns more and they'll start accumulating this trait, takes on average 7 turns to max once you qualify for the trigger, but as you can see it can take awhile to qualify.
Note that the 2 traits above the trigger is time in region, not turns idle, so you can feel free to move your priests around in the region once they get there.
3) Monk Ancillary (Pagans get 'Zealous Disciple' instead, muslims can't get either). This I'll actually go for as its quick and easy to get. (Also, see the trigger for the Dogmatic trait line below, you do pretty much the same thing to get Dogmatic as you do for Monk, except the region needs >85 own religion rather than >=70).
Gives 1 Piety. Trigger: Park in region >3 turns (must be IDLE, so do NOT move), ReligionShift<=10, PopOwnReligion>=70, 50% chance per turn after you meet the requirements, and you can NOT get it on any priest that has Royal Seminarian, they are mutually exclusive.
Its possible to get this while going for Purifier, if your religionshift is slow, but if he doesn't get it before ReligionShift>10, you'll have to move him later to another region to get your Monk. Note the "religionshift<=10" part of the trigger, you do NOT want religionshift when going for this trait. So, after your priest finishes maxing out Purifier, move him to a region that already has high % own religion (at least 70 but preferably >85) and just let them sit until they get their Monk. Easy to get, on average takes 6 turns, note again priest must be IDLE and not merely in region (turn 1 move in region, turn 2-4 sit idle, turns 5+ sit idle and 50% chance per turn to get Monk).
4) Strong Faith trait line. This is the Growing Faith, Strong Faith trait line. You can get +4 Piety here, but really only the +1 or +2 are worth going for, gets very difficult to get the higher levels of this trait. Also, there's an Anti-trait that can subtract from this but its conditions are so near impossible to meet that'll you'll likely never see it happen (among other things, priest would need to be in region >5 turns and still have % heresy>20).
Gives: Piety 1,2,3,4, Thresholds 1,4,8,12
There are 3 different triggers for this, 2 are easy the 3rd takes work. Also, there's an 8% chance for any priest to be born with +1 of this trait (pure random chance), and also a 60% chance of a +1 for any priest born in a city with a Cathedral or better.
a) Accept Great Council event. All priests <60 distance from Capital have a 25% chance to get a +1 (takes effect next turn).
b) Park your Priest in Jersulam province for more than 1 turn (if not pagan), Mecca for 3+ turns (if muslim) or Embi for 3+ turns (if Cuman), there's a % chance per turn after that to improve this trait (33%, 40%, 50% depending on province). However, you can ONLY get to Strong Faith this way, you will get no gain for this trait line beyond Strong Faith by sitting in these provinces.
c) Move a big pack of priests into a province with low PopOwnReligion for 4 turns, trait gain based on fast religion shift in a short period of time, only first 4 turns in a province count. There's actually 3 triggers related to this, the point of all of them is to get a LOT of religion shift (>8 or >10 depending on trigger) in <5 turns. There's an 85% chance of +1 per turn during the first 2 turns if you can get >8 shift that fast, and an additional 33% chance per turn of +1 once >10 shift is achieved for priests with 0 skill in this trait, otherwise its a 25% chance once you have at least Growing Faith. So, move your pack of priests in all on the same turn (and write down which turn it is), leave them there 4 turns then pick another province to move to.
Note the thresholds again, 1,4,8,12, so you need +4 gain to improve from Strong Faith to the next level, and then another +4 gain to max the trait line. Very hard work to max. IMO worthwhile and easy to get Growing Faith, not too bad to get Strong Faith, you've got far more discipline than me if you can get +3 or +4 piety out of this trait line.
5) Good Denouncer. This is the trait line you get for Denouncing Witches or Heretics. There's an Anti-trait line Bad Denouncer for when you fail but live. Not many are aware of how these particular anti-traits interact: the key is that once you get a point in either you can't get any gain in its opposite (the trigger includes a line "and not Trait BadDenouncer > 0", similar for the antitrait). So, if you get Servant of God or better, then there is never ANY penalty for failing to denounce (still can go heretic, but you'll never lose points in Good Denouncer once you get your first +1 on it). Likewise, if you get Poor Prosecuter or worse, then you can never get rid of the Bad Denouncer or gain in Good Denouncer no matter how many successful times you Denounce.
Effect: Piety +1,2,3,4,5, Thresholds 1,2,4,8,12, for Good, Piety -1,-2,-3, Thresholds 1,3,6 for Bad. The chance is 85% for Good if you succeed, 33% for Bad when you fail. So, the tactic is, if you don't have the trait line at all on a priest, try to get a good % chance of mission success for his first Denounce, to get the Good trait line. Once he has the trait line, feel free to take more risk. If he gets the Bad line, he can't get Good and over time Bad will get worse if he keeps Denouncing, so either don't order it or treat him as expendable and give him the long odds missions until he goes heretic and build a new priest.
6) Dogmatic trait line. Anti-trait Open Minded. There's only 1 Piety available on this line, and you need the 2nd lvl or better of the trait to see it, but its interesting because it is really about giving Orthodox/Unorthodox (+1/-1 per level of the trait), and also HeresyImmunity (if you max the trait line), both of which effect the chance of your priest becoming a Heretic. Also, some interesting triggers. This trait is the only reason to ever leave a priest inside a city (The removed the Archbishop Ancillaries, and all those posts you've seen about having a priest with your General, either in a city or in the field, will help the general are nothing but Myths, there is no effect from this at all), and you can get the anti-trait simply by ending turn next to a heretic/witch.
Gives Piety 0,1,1, Thresholds 1,3,6, Anti-Trait has no effect on Piety, Thresholds 1,2,3. The description seen on your panel in game is "Orthodox Priest", "Dogmatic", "Utterly Dogmatic" for Dogmatic, "Odd-Habits", "Open-Minded", "Quite_Unorthodox" for Open Minded trait. Level 1 is easy to get, but gives no piety, lvl 2 gives the +1 Piety but takes a bit more work.
Triggers:
a) 15% Chance per turn of +1 if you end turn in a city with Cathedral or better (Catholic or Orthodox only)
b) 100% Chance of +1 if Great Council accepted and <60 from capital (actually takes effect at turn end, so it'll appear on your priests info panel the following turn)
c) 33% Chance on the 3rd turn in a region (only) if ReligionShift<10 and PopOwnReligion>85 (note the similarity of this trigger with the tactic for getting the Monk ancillary). This is a decent way to build the skill, you just need 2 adjacent regions of >85 Ownreligion and remember to move across the border, spending 3 turns in each region. Though, odds are better sitting in town at 15% per turn (which = 38.5% of at least 1 skill gain over 3 turns).
c) Antitrait trigger: 20% Chance of -1 if in region >2 turns and PopOwnReligion<=40 (another reason to move your priests in groups, or even packs, make the religion shift happen fast and you'll reduce your chance to get this bad trait).
d) Antitrait trigger: 20% Chance of -1 if "CharacterNearHeretic". I'm not sure exactly what qualifies for this trigger, always assumed its when you end turn adjacent to a Heretic/Witch.
7) Bishop, Cardinal, Patriarch (and Archbishop).
a) There is a new game script in SS 6.3 for making some of your Priests 'Bishop'. +1 Piety. You will get 1 Bishop per province that has at least the lvl 1 church, or castle church, building (note again that abbey and cathedrals increase the priest agent limit by 2). So, most of your priests will be bishops now.
b) Cardinal, as in being in the College of Cardinals, also +1 Piety but replaces the +1 from Bishop (if he was one), so not cumulative.
c) Patriarch. This is for Orthodox faction only. +2 Piety, limit of 1 priest per faction will get this, by game script (seems pretty basic, gives it to the first priest in your agent list regardless of anything if you're Orthodox and don't already have a Patriarch). I'm not entirely clear on this script, might be mistaken on it.
d) Archbishop Ancillary. Sadly, these were removed in SS6.3 (existed up to 6.2), which is a shame as they were fun and useful (gave both piety and a movement bonus, and there were good and bad ones, and gave a reason both to sit priest in city and to NOT sit priest in city depending on which Archbishop you had, if any, and whether the city had Cathedral or better).
8) Witch Hunter Ancillary. Piety 1, Unorthodoxy -1 (Orthodoxy/Unorthodoxy work like chiv/dread, so -1 Unorthodoxy = +1 Orthodoxy and reduces chance your priest goes Heretic). IMO this ancillary is nearly impossible to get and therefore not worth going for, except for the chance to get it when your priest is born. Triggers:
a) 10% Chance at birth if Faction Leader has the trait ReligiousActivity>1 (ie. Not merely "Religious" but at least "Dutifully Religious" or above)
b) Park in region>6 turns, 20% Chance per turn thereafter so long as PopulationHeretic>15. Extremely hard to get since PopHeretic will likely drop below 15 long before the time in region requirement is met.
9) Divine Protection trait line. Piety 0,1,2, Thresholds 1,3,6. Gain by surviving assassination missions if assassin
dies. Extremely rare to get to level 2 of this trait to see some piety, since AI isn't often active with assassins, doesn't target priests much when it is, and your priest would need +3 to threshold to reach lvl 2 of this trait to see a +1 Piety and would certainly be killed before getting it.
10) Knight Crusader Ancillary. Does not give Piety. Gives +2 Security and +1 Violence. Move priest into region that is a Crusade target, park there >2 turns, then 33% chance each turn.