How To Become Curia Controller in EU4

Controlling the Curia is the prime reason for choosing the Catholic faith. The multitude of bonuses it provides are awesome, but you need to work hard to get them.

The only way to secure control of the Curia for your nation is to amass Papal Influence and invest it. You invest papal influence by pressing the leftmost button on the top of the Papal Interface tab. This tab is located on the bottom left of your screen, near the minimap.

Note: Investing papal influence through the papal interface is the only way to become Curia controller.

Amassing Papal Influence

Papal influence is not easy to come by.

Catholic nations should prioritize obtaining as much of it as possible.

You can save up to 200 papal influence at a time. The Papal State does not amass Papal influence, using another mechanic to wrestle control of the Holy See instead.

Passive Accumulation

Things that impact papal influence are:

• Base yearly increase of +0.5
• Events, decisions, and mission rewards
• National Ideas (usually +2, +1, or +0.5 yearly papal influence)
• Defender of the Catholic faith (+1 yearly)
• Having the triggered modifier “Crusade” (+1 yearly)
• Loyalty of the Clergy estate (up to +1 yearly)
• Each controlled Cardinal provides +0.5 yearly
• Violating the treaty of Tordesillas (-10 yearly)
• Being excommunicated (-10 yearly)
• Occupying Rome (-10 yearly)

This yearly change is then modified by the Papal State’s opinion of you. It ranges from -100% at -200 relations, up to +100% at +200 relations.

This means that you should attempt to keep relations with the pope as high as possible, even allying him. Having a positive opinion of you also renders you immune to excommunication.

Actively Gaining Papal Influence

Aside from events and mission rewards giving you a flat increase, the easiest way to actively gain papal influence is through converting provinces.

Converting a province to the Catholic faith nets you papal influence depending on its development.

This is the reason that colonizing nations have an easy time amassing Papal influence. Simply converting your colonial nations’ heathen land to Catholicism will give you lots of papal influence.

This mechanic encourages Catholic nations to resort to conversion to attain religious unity. Of course, you can go the tolerance route, raising your tolerance of heathens and heretics, but your papal influence will suffer considerably.

Spending Papal Influence

After accumulating Papal Influence, you can spend in the Papal Interface tab.

There you have a choice between unlocking one of the passive bonuses for 20 years or investing into your chances to become the next Curia Controller.

The Temporary Bonuses

The temporary bonuses, also called “Curia powers” each cost 50 influence.

These bonuses are:

Sanction for increased taxes
Construction cost -10%
National tax modifier +15%

Forgive usury
Yearly inflation reduction +0.1
Interest per annum -0.25
Yearly corruption -0.04

Bless ruler
Morale of armies +10%
Yearly prestige +1

Proclaim holy war
Manpower recovery speed +15%
Land maintenance modifier -5%

Sanction dynasty
Yearly legitimacy +1
Improve relations +10%

Send papal legate
Diplomatic reputation +1
Diplomatic annexation cost -10%

Beatify local saint (costs 100 influence)
Gain 1 stability

Sanction commercial monopoly
Gain 1 mercantilism

All of them require you to be at peace with the Papal State, but they do not stop applying if you end up at war with them while they are active.

All these bonuses are strong, and you should activate them whenever they fit your current needs.

For example, when annexing a large vassal (or many vassals) you should activate the “papal legate” bonus. If fighting a close war, the “bless ruler” bonus can help you turn the tide in your favor.

Investing for Curia Controller

Your other option is to invest your accumulated influence towards the Curia. You need at least one Cardinal in your lands to use this interaction. Pressing the button on the top left will spend 5 influence and invest it towards becoming the next controller.

Every subsequent click costs 5+ 0.5*(amount already invested) and gives you 10 invested influence. So, the second click costs 10, the third 15, the fourth 20 and so on.

When Should You Invest?

The amount you get by investing for the Curia is always 10. This means that the less you have already, the more it is worth investing. I suggest clicking the button at least 3 times.

From that point on you should focus on unlocking the various bonuses available to you for 50 papal influence.

Your chances to become the next controller are a percentage of your invested influence relative to the total influence invested. It is generally easier to lock the spot of Papal controller after the reformation, as the number of Catholic nations drops significantly.

Investing as the Papal State

The Papal state does not make use of the influence mechanic. They instead accumulate investiture towards being the next controller by utilizing their own mechanics.

These are:

1. Using the “appoint cardinal” diplomatic action
Simply go to the “papal actions” tab when initiating diplomacy with a Catholic nation. As long as they have a province with more than 10 total development, you can appoint a Cardinal there for a monetary cost.

Should you be the Curia Controller, that cost can come straight from the Curia treasury and not yours. The cost depends on the total number of Cardinals and the number of Cardinals the target nation already controls.

Successfully appointing a Cardinal raises relations with the target nation and nets you +10 invested towards being the next controller.

2. Using the “appoint loyalist as Cardinal”
From the Papal Interface, click the button that other nations use to invest influence.

It will prompt you to increase your corruption by +0.5 and pay a cost depending on the number of Cardinals you control and in total, in order to generate a Cardinal in your own lands. This cost always comes out of your own pocket.

Each such Cardinal will increase your investment towards becoming the controller by +1 yearly.

3. Calling the Ecumenical council
The Papal State cannot use the “buy indulgences” button available to other Catholics. Instead, they get another button in its place which spends money from your own treasury, enriching the Curia coffers by a quarter of that amount and giving you 10 investment towards the next Curia election.

Advantages of Controlling the Curia

Controlling the Curia provides the following passive bonuses:

• +1 Diplomat
• +1 Yearly prestige
• -10% Stability cost modifier
• +2 Possible advisors
• -20% advisor cost
• +1 leader without upkeep
• -20% aggressive expansion
• -5% technology cost
• 10% clergy loyalty equilibrium

On top of that, it allows you to excommunicate nations, call crusades, and enact a Golden Bull.

The reduced aggressive expansion and advisor cost can give your nation a massive boost in the early game.

As the Papal State, maintaining high prestige and remaining as Curia controller, you can bring the entirety of Italy under your control very fast.

Excommunication

The Curia controller can excommunicate any nation that the Papal State has a negative opinion of, as long as said nation has less than 50 papal influence and is not the current Defender of the Faith.

The excommunication can be lifted if the nation obtains good relations with the Papal State or buys indulgences. It is also aimed at the leader, not the country.

This means that if the ruler changes, the excommunication does not have an effect anymore.

Excommunication penalties:

• -2 Yearly prestige
• -10 Yearly papal influence
• -5 Yearly devotion (if a theocracy)
• -3 Tolerance of the true faith
• -5 Relations with Catholic nations
• -200 Relations with Catholic theocracies

All Catholic neighboring nations gain a unique “Excommunicated ruler” casus-belli against the target which allows for the conquest of provinces and vassalization at very little aggressive expansion.

Excommunicating your rivals and nations you are aiming to expand into is a very good idea. It ensures you will accumulate little to no aggressive expansion while conquering a lot of land.

Crusades

Another Papal action from the diplomacy menu is calling a Crusade. You can target a single heathen nation that the Papal State has less than -50 relations with to call a crusade against. This is available only before the Age of Absolutism.

Catholic nations bordering the target get a “Holy war” casus belli against them, while all Catholic nations at war with the target get:

• +30% National manpower modifier
• +10% National tax modifier
• +10% Morale of armies
• +1 Yearly prestige
• +1 Yearly papal influence
• +0.25 Yearly devotion

Golden Bulls

The Papal controller can use 400 ducats from the Curia coffers to give a bonus to all Catholic nations.

These are:

Illius Qui Se Pro Divini (after Age of Absolutism has begun)
-10% Aggressive expansion impact
Enables Crusades after Age limit

Apostolicae Servitutis
-50% Curia powers cost

Christiana Pietas
+2 Tolerance of Heathens
-5% Development cost

Immensa Aeterna Dei
-10% Institution embracement cost
+25% Institution spread
Cardinals spread institutions

Libertas Ecclesiae (only as the HRE emperor with Catholic as the official faith of the empire)
+20% Imperial authority growth modifier
+15 approval of reforms by Catholic princes

Dei Gratia Rex
+0.5 Yearly absolutism
-2 Unrest in true-faith provinces
-25% Regiment drill loss

All of them have their uses.

If you need an institution to spread to your lands, “Immensa Aeterna Dei” is awesome. The AI will also choose it by default if they haven’t embraced the most recent institution.