Understanding forts and zones of control

[Bitslinger]

I and many others have a hard time to make sense out of zones of control (zoc). There is no in-game guide, the wiki is severely lacking and I was unable to find a single, (mostly) complete guide on how it all actually works.

I will start out with what I know and what still confuses me. I hope others will do the same and we will finally get a handle on this. I will update the first post to include everything new I learn and hope it will transform in a comprehensive guide over time. Please help us out.

Do not use this thread to complain about forts, fort-prizing, zone of controls or anything else. This should be about understanding how it works, nothing else.

Sieging, ticks and garrisons
Coming soon.

Terrain penalty
If an army is besieging a fort is attacked, the terrain penalty will apply to the besieging force, not the relieving (attacking) one. This applies to the crossing penalty as well. It does not matter over what crossing the relieving force is attacking. Yes even coming per ship will have no negative consequences. Crossing penalty will depend on how the besieging force entered the province. The UI does not show where the besieging force entered the province.

What to do: If the enemy is heavily fortified try to wait for their troops to enter your lands, instead of invading / sieging immediately. Build / keep mountain forts. Try to enter sieges without crossing whenever possible. Try to remember it, if enemy forces came via ships or strait crosses to besiege forts. Have reinforces ready if you need to siege mountain forts.

The basics of zones of control

A zone of control restricts the movement of enemy armies through the province with the fort, and provinces immediately adjacent to it.

It will only work with adjacent provinces that are allied with the fort controller or neutral. Movement in provinces controlled by the enemy will not be limited.

After an enemy army enters a province within the zone of control, they can only move from there to two other provinces: the province containing the fort, and the province they came from.

As I understand it currently, it is also possible to leave to any neighbouring province that is controlled by allied forces.

This means that forts form a barrier against enemy armies; if placed so that there's no way around the fort(s) the enemy is forced to siege one or more forts in order to get at the rest of one's country. This can provide time to muster up one's forces, or simply time for the enemy to get hurt by attrition while sieging. The Zone of control also applies for occupied forts. An army who belongs/allied to the province owner can not pass as long as the fort is not liberated.

Understood weirdness

Moving into forts through overlapping zones of control
Assume that fort F and fort G both project a zone of control on a province. To reach fort F you have to go through the province. While both forts are in enemy hands this is perfectly fine and you can do so. If you march an army onto fort F and capture it successfully but ignore fort G, you can no longer move from the province to fort F, because the zone of control by fort G will block the movement. Your troops could be stuck behind enemy lines, after they completed the siege.

What to do: Capture fort G first, if you can reach it without going through overlapping zones or capture the province and make sure to keep it. This means having troops either in the province or besieging all forts projecting a zone of control on it.

Spoiler: Example, big picture

Yes, there is a fort hiding beneath the tooltip, projecting a zoc and stopping our troops.

Leaving zoc into friendly provinces can be used to hop over forts
If a enemy fort is between two friendly provinces, allied armies can walk all over it.

Spoiler: Example, big picture

Luxembourg will not block our way!

AI "shortcuts"
If an ai controlled army can reach (and wants to go to) any province, it will take the shortest possible path. It takes zones of control into account while determining if it can reach a province, but not while following the shortest path. So it will not reach places made unreachable via forts, but it will not walk around forts if it could. They will walk right through.

This is a bug and known to Paradox. Hopefully they will fix it soon.

To be fair #1 is a bug somewhere in gameplay code and it would be a pretty stupid/pointless cheat (and we would have added defines for it like with #2 if it was intended). [...] I know these issues are getting further looked on so all hope is not lost, necessarily.

Not yet understood weirdness (please help out)

Ignoring border forts (not the ai "cheat", not "hop over" described earlier)
It is sometimes(?) possible to ignore zones of control, if the entered zone of control province / fort and the otherwise illegal exit province are both neighbouring allied provinces. Can someone confirm this? Does it always work?

Spoiler: Example, big picture

More border-weirdness

Spoiler: Big picture

Yes, I used this picture further up to explain something I believe I understand. Here is something I don't. Moving troops directly from Barrois into Metz is not possible. Moving troops from Trier into Metz and from there to Barrois is. I do not get why; for all I can see the situation is perfectly symmetrical and it should work both ways.

Anything else someone is still unable to understand? Found something that proves rules stated here wrong? Post it!

 

[:Philippe_CVP]

 

[grotaclas]

This thread is from 2016 and the video is from 2017. They are both very outdated and don't reflect the current situation. The AI "shortcut" bug was fixed sometime around 2017 and the distance-of-two rule which is the major point of the video, was removed in version 1.32(form 2021). There were also several other rules changes in early 1.3x versions(e.g. you can now move to adjacent provinces which you control, as long as you are not on a fort)

 

[:Philippe_CVP]

ok thank you. but where can we find the rules of this game.

 

[:Philippe_CVP]

and if possible not a video.

 

[grotaclas]

ok thank you. but where can we find the rules of this game.

Nowhere. So far I have not seen anybody who knows all the movement rules(not even the developers, because they were created by multiple generations of developers over the lifetime of the game). I probably investigated more than 90% of them, but I have forgotten parts of these investigations and I can't write down all the rules. From time to time I discover rules which I have never seen before. And I didn't investigate all the details of each rule(e.g. if they apply equally to subjects and war allies and subjects of war allies and if it matters if the subjects are part of the war or the war allies are also actual allies.

 

[:Philippe_CVP]

Thank you very much for the time you took for answering me. I am a little bit disappointed because forts are not the only problem I have with this game. Many things are not clear because not explained and I am fed up with trying to guess. It's a common problem with all paradox games. Crusader Kings III is a little bit better for that with the system of multiple windows to define the concepts and mechanisms. I already gave up with Hearts of iron IV . And I will probably do the same soon with EU IV. Also I don't like watching video on Youtube they are often a waste of time.

 

[grotaclas]

Thank you very much for the time you took for answering me. I am a little bit disappointed because forts are not the only problem I have with this game. Many things are not clear because not explained and I am fed up with trying to guess. It's a common problem with all paradox games. Crusader Kings III is a little bit better for that with the system of multiple windows to define the concepts and mechanisms. I already gave up with Hearts of iron IV . And I will probably do the same soon with EU IV. Also I don't like watching video on Youtube they are often a waste of time.

Have you tried the wiki? The eu4 wiki is very detailed and explains almost all game mechanics. Most of the explanations are correct and most of the others are correct enough if you are not one of world's best players who wants to do something which nobody has ever done before

 

[:Philippe_CVP]

yes I know the wiki but I don't know if it is up to date or not.

Zone of control​

Aller à la navigationAller à la recherche
Please help with verifying or updating older sections of this article.
At least some were last verified for version 1.28.

Please help improve this article or section by expanding it with: Information about the many changes to the movement rules since version 1.31.

Forts limit unit movement due to their zones of control ("ZoC"). This article explains precisely how they used to work in version 1.28.

 

[grotaclas]

yes I know the wiki but I don't know if it is up to date or not.

Zone of control​

Aller à la navigationAller à la recherche
Please help with verifying or updating older sections of this article.
At least some were last verified for version 1.28.

Please help improve this article or section by expanding it with: Information about the many changes to the movement rules since version 1.31.

Forts limit unit movement due to their zones of control ("ZoC"). This article explains precisely how they used to work in version 1.28.

That article is outdated. But it is difficult to update it, because nobody knows the rules. But most other mechanics didn't change since they were last verified and the ones which did change, only changed in minor ways which only matter in high-level play or if you try to calculate something exactly.

 

[wthree]

Something worth adding into a guide about sieging and forts is that the AI gets a relatively large bonus to sieging.

 

[grotaclas]

Something worth adding into a guide about sieging and forts is that the AI gets a relatively large bonus to sieging.

What makes you think that?

 

[wthree]

What makes you think that?

At first it was just a general suspicion, but I tested it.

Edit: To clarify, the AI is able to siege down provinces much quicker than the player, despite a range of bonuses being against them. So there must be a hidden bonus.

 

[grotaclas]

At first it was just a general suspicion, but I tested it.

How did you do that? What were your results? Which other factors did you take into account which could explain your results, but which would not be a "relatively large bonus to sieging" which is specific for the AI? How did you make sure that these factors didn't influence your results?

 

[wthree]

How did you do that? What were your results? Which other factors did you take into account which could explain your results, but which would not be a "relatively large bonus to sieging" which is specific for the AI? How did you make sure that these factors didn't influence your results?

So I attempted to limit the amount of variables (i.e from other bonuses) by testing at the start of the game, i.e before any siege bonuses might come into an effect. I played as France, in separate wars against neighbours (specifically Burgundy, England, Aragon and Castile). I played as France so I could test with and without artillery, although the AI didn't have them at this stage. The basic test was to start a siege of enemy territory at the same time as an AI, with several different counties in France and the above nations. The basic concept was to see how many times the AI sieged a county before I did, and then go from there. I tried with a range: my 3 siege pip leader with either 3 or 0 artillery, against enemy armies with siege pips between 0 and 3.

The AI won 100% of the time over the course of 63 sieges.

 

[grotaclas]

I tried with a range: my 3 siege pip leader with either 3 or 0 artillery, against enemy armies with siege pips between 0 and 3.

The AI won 100% of the time over the course of 63 sieges.

Are you saying that your sieges with Jean Bureau, who has 3 siege pips and +15% siege ability, were slower than the AI sieges who had no siege pips, even if you had 3 artillery as well? I just tried it two times by sieging Picardie while Aragon sieged Narbonnais and I was about twice as fast both times. Here are screenshots from the second time(I reloaded the save from the day when the AI siege started(my siege had started two days earlier):

There are many things which you didn't take into account. E.g. the +15% siege ability from Jean Bureau, the luck modifier which Castile and England have(unless you disabled/changed lucky nations), the siege penalty from not having a blockade(in my test I had that penalty while Aragon didn't have it for most of their siege), different fort defenses from local modifiers and many more which can be available at the start of the game. They can skew the chances quite heavily in one direction or another. If you post a save from when such a siege is about to start(or has just started), I can probably tell you more about why you are losing the sieges. My guess would be that there is something strong which favors the AI in your test game(e.g. from a mod), but not the AI in general.

 

[FrogCrusher]

I really think there is a general problem with dice role in siege though. I already wrote about that but were told "confirmation bias".
But sorry, having to do 6 ticks at 47% success chance, or even raising very oftent at 75/80% chance is a pure statistical anomaly. It happens to me far too often to see siege situations (both for me and AI) that are 1 chance over 1000 to happen.

I do remember at some point there was a bug either on the life time of ruler in republic or the dice role bonus of the leader in republic (don't remember exactly which one). The people who discovered that bug were bombed with "confirmation bias" message until it was confirmed by PDX there was indeed a bug with RNG in that specific domain. That was fixed later in a patch.

So I'm not saying the AI is cheating, it's not my PoV. But I still do continue saying the dice roll are not evenly distributed as they should be. Same story with advisors when you can have very often the exact same type months after months when you fired them.