EU4: Are Forts Worth Using?

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Forts are necessary and worth it, but don’t maintain too many or your economy will suffer. You pay a monthly overhead of 1 ducat per fort level. This becomes a burden when you have multiple forts, so you want to be smart in their placements.

A fort’s worth can be measured in three metrics:

  1. Position
  2. Defensiveness
  3. Attrition

I. Position Details

The best forts are those that prevent or delay enemy movement.

Forts project a zone of control (ZoC) around their adjacent provinces. An enemy army can enter these provinces, but can’t go through to the next unless they take the fort.

You only need forts in key positions.

It’s unnecessary to cover your entire nation with them.

Look for provinces between impassable terrain or that overlook straits and narrow passages. These provinces usually have features with good defensive modifiers.

The Mountain Fort of Malaga Guards the Straights of Gibraltar / EU4
The Mountain Fort of Malaga Guards the Straights of Gibraltar

Fort Traps

Forts can become death traps by taking advantage of these rules:

  1. An enemy army only has one way in or out of a fortified province.
  2. When attacking an enemy who’s sieging a fort, you’re always treated as the “defender” during combat.
  3. An “attacker” gets a -1 combat penalty when fighting in these terrain:
  • Glacial
  • Forest
  • Woods
  • Highlands
  • Hills
  • Marsh
  • Jungle
  • Mountain (-2 combat penalty)

If you have a fort on any of these terrains, you can purposely wait for your enemy to siege it. You then move your army around them and attack from the entry point. You’ll have a guaranteed combat advantage against them.


II. Defensiveness

Defensiveness extends the time of each siege phase. A fort with high defensiveness can potentially force your enemy to waste years trying to siege it.

These are the common sources of defensiveness:

Defensiveness Modifier Source Modifier Type
+25% Mountain Terrain
+10% Hills Terrain
+10% Highlands Terrain
+0.1% per point Power Projection Power Projection
+10% Salt Provincial Trade Good
+15% Ramparts Manufactory
+33% Defensive Edict State Edict

III. Attrition

Armies always take at least 1% monthly attrition damage when sieging a fort.

This stacks with attrition taken from supply weight problems and inhospitable climate.

When you combine this with high defensiveness, you can drain your enemy’s manpower indefinitely. This hurts their war enthusiasm and war exhaustion, and decimates their military potential even before you engage them directly.

Defensive terrain typically has fewer supplies for armies.

Mountains provide the lowest supply, which further makes them the ideal places for forts.


General Pointers on Forts

When building forts, be mindful of these tips:

  • Forts on flat terrain should be dismantled unless they control a chokepoint. Their lack of defensiveness means they’ll fall quickly and easily.
  • Compared to states, territories are less impactful to your war score and war exhaustion when occupied. You can leave them unfortified unless they’re a chokepoint.
  • Forts prevent rebels from affecting your provinces’ unrest. They also help provinces recover from devastation.

Review your fort placement regularly, especially after conquering new provinces. These new provinces may have forts that are redundant in your national defense plan. Dismantle them so you won’t have to pay for their maintenance costs.

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Louie Nelson Zafico

As a frustrated otter who dreams of getting published, Louie instead wastes his life cuddling his cats. He spent his childhood playing Suikoden, grew up with Total War, and matured (somewhat) with EU4. He hopes to someday find a geopolitical JRPG with the 4X systems of a Paradox game.