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Please help with verifying or updating older sections of this article. At least some were last verified for version 3.8.

This article is for the PC version of Stellaris only.

Subterranean Civilization is a colony event chain that has a very small chance to trigger 2 or 3 years after any colony has been founded. It can only happen once per game. The event chain offers two mutually exclusive paths which both have eventual rewards and drawbacks. The hostile path can also be followed should peace fail.

Seismic Disturbances


There have been many reports of unexplainable seismic disturbances on [colony name]. Tremors can be felt across the [planet or moon], and many of our settlements have suffered damage. While investigating the earthquakes, our scientists discovered a vast network of subterranean caverns.

The deepest of these caverns are home to some kind of indigenous civilization, and they appear to be tunneling towards the surface! Ground vibrations from our settlements may have triggered this behavior, but we cannot be certain. There is no telling how these aliens will react when they spill out of their tunnels and encounter our colonists!

 
Trigger conditions:
  • Not capital world
  • Colony is not on a Ringworld, Habitat, Ecumenopolis, Relic or Tomb World
Mean time to happen:

Time 30 months


We have to deal with the situation.
  • Issue Special Project: Establish Communications
  • Issue Special Project: Preemptive Strike
Exterminate!
  • Issue Special Project: Preemptive Strike

Special Project Completed


One of our probes burrowed through the ground and intercepted the tunneling aliens on [colony name]. After the startled alien workers calmed down, the probe was successful in establishing communications with their leaders.

 
Trigger conditions:
  • Seismic Disturbances
Is triggered only by:

Finishing the Establish Communications special project


Open a channel.
  • Subterranean Civilization modifier added, giving the following effects: Society Research from Jobs +10%
  • Adds a Subterranean Contact Zone planetary feature to the colony

Special Project Completed


Our efforts to destroy the subterranean aliens on [colony name] have met with success! We managed to collapse several of their tunnels on top of their workers, and the caverns that housed their cities have been flooded with nerve gas.

Casualty projections are close to 100%, and our security forces are confident they will be able to deal with any surviving stragglers.

 
Trigger conditions:
  • Seismic Disturbances
Is triggered only by:

Finishing the either the Preemptive Strike or Destroy Subterranean Civilization special project


Compliments to all service branches involved.
  • Adds a Subterranean Farming Caverns planetary feature with a removable Blocker
  • Adds a Subterranean Generator Areas planetary feature with a removable Blocker
  • Adds a Subterranean Mining Sites planetary feature with a removable Blocker

Famine


We have been approached by a delegation from the subterranean aliens on [colony name]. It seems their empire has fallen on hard times recently, and they are facing the threat of a famine. They are pleading with us to provide whatever assistance we can.

 
Trigger conditions:
  • Finished the Establish Communications special project
Mean time to happen:

Time 240 months


Of course. We will help however we can.
  • Food: −50
  • Relations with the subterranean civilization improved
They'll have to fend for themselves.
  • Relations with the subterranean civilization harmed

Subterranean Expansion


We have finished clearing out the nerve gas and the dead alien bodies from the tunnel network on [colony name]. It should now be safe for our colonists to move in. The primitive cities the aliens left behind will be demolished, of course, and replaced with our own advanced architecture.

 
Trigger conditions:
  • Finished the Preemptive Strike special project
Mean time to happen:

Time 240 months


Excellent.
  • Subterranean Cities modifier added, giving the following effects: Max Districts +3

Subterranean Refugees


A large group of refugees from the underground alien empire on [colony name] recently streamed out of their tunnels onto the surface, chased by a small army. They are apparently part of some sort of religious minority, and claim to be fleeing persecution.

If we let them join our colonists on the surface, it will no doubt anger the rulers of the empire they fled from. However, if we let the pursuing army take them back underground, they will likely face mass execution.

 
Trigger conditions:
  • Finished the Establish Communications special project
Mean time to happen:

Time 240 months


Let them join our colony if that is their wish.
  • Adds 1 Pop from a random species to the colony
  • Relations with the subterranean civilization harmed
We can't afford a political incident. Send them back.
  • Relations with the subterranean civilization improved

Survivor Pocket


Our forces on [colony name] are still mapping the tunnel network below our colony. They have come upon a large city belonging to the subterranean aliens that managed to isolate itself from the rest of their underground empire before we flooded it with nerve gas. There are millions of frightened aliens in the city. Should our engineers collapse the cavern to finish the job?

 
Trigger conditions:
  • Finished the Preemptive Strike special project
Mean time to happen:

Time 240 months


Fanatic AuthoritarianFanatic Xenophobe No! Bring them to the surface, where they shall serve us.
  • Adds 2 Pops from a random species with the Slaves citizenship species rights to the colony
Yes. Put them out of their misery.

Gift


As a gift to celebrate the friendship between our two civilizations, a caravan from the subterranean aliens on [colony name] have brought a large quantity of gemstones to the surface. Stones such as these are apparently mined by their empire deep underground, as close to the [planet or moon]'s core as they dare to venture.

 
Trigger conditions:
  • Finished the Establish Communications special project
  • Relations with the subterranean civilization have never been harmed
Mean time to happen:

Time 240 months


How kind.
  • Minerals Gained: 100-1000

Gold


Prospectors have ventured into some of the deeper tunnels that once belonged to the now dead subterranean aliens on [colony name]. They have finally discovered the long-rumored gold mines where it was believed the underground alien empire acquired its large reserve of precious metals!

 
Trigger conditions:
  • Finished the Preemptive Strike special project
Mean time to happen:

Time 240 months


Excellent.
  • Energy Credits Gained: 100-1000

Xeno Anthropologists


Several xeno anthropologists from [capital name] have returned to the surface of [colony name] after spending a great deal of time living among the subterranean aliens native to that world. They have learned much about their ancient ways and customs, which will no doubt benefit our society research.

 
Trigger conditions:
  • Finished the Establish Communications special project
  • Relations with the subterranean civilization have never been harmed
Mean time to happen:

Time 240 months


Excellent.
  • Society Research Gained: Society research 350-1000000

Treasury


Scout units exploring the tunnel network on [colony name] have entered the royal palace in what was once the capital city of the underground alien empire. The corpse of what passed for their emperor is still perched on a massive throne in the main chamber.

After using explosive charges to breach the palace treasury, our scouts found it filled with gold and strange alien art. The art will be shipped back to museums on [capital name], and the sale of the gold should provide a nice boost to our state budget.

 
Trigger conditions:
  • Finished the Preemptive Strike special project
Mean time to happen:

Time 240 months


Excellent.
  • Energy Credits Gained: 100-1000

Earthquakes


There has been a wave of earthquakes on [colony name] recently, and buildings in several of our settlements have collapsed with many fatalities as a result. The subterranean alien empire is excavating a new cavern deep underground where they plan to build a new city, and this appears to be the source of the earthquakes.

 
Trigger conditions:
  • Finished the Establish Communications special project
Mean time to happen:

Time 240 months


Turn the other cheek.
  • The colony gets +10 Devastation
  • Angry modifier added for 120 months, giving the following effects: Happiness −20%
We must demand an apology!
  • The colony gets +10 Devastation
  • Relations with the subterranean civilization harmed

Earthquakes


[colony name] has been racked by another wave of earthquakes recently. It seems that some of the deeper parts of the underground tunnel network has collapsed without the subterranean aliens to maintain it. Many of our settlements have suffered damage.

 
Trigger conditions:
  • Finished the Preemptive Strike special project
Mean time to happen:

Time 240 months


Unfortunate.

Message Delivered


Trade with the subterranean aliens on [colony name] has dried up as of late, with their caravans showing up more and more seldom. Today we received a message from a representative of their military. They don't seem very pleased.

 
Trigger conditions:
  • Finished the Establish Communications special project
  • Relations with the subterranean civilization have been harmed twice
Mean time to happen:

Time 20 days


Let's see it.
  • Subterranean Civilization modifier removed
  • Removes the Subterranean Contact Zone planetary feature

Subterranean Invasion!


The subterranean aliens on [colony name] have emerged on the surface! Large armies equipped with primitive yet lethal projectile weapons are spilling from the tunnels, and their vanguard has already begun an assault on our settlements.

Our security forces are responding, but we may need to send reinforcements!

 
Trigger conditions:
  • Message Delivered
Mean time to happen:

Time 35 days


To arms!
  • 6-12 industrial armies invade the colony

Victory


Our forces have managed to drive the subterranean aliens on [colony name] back into their underground lairs, and they are contained for the moment. This is a temporary solution, however, and it is only a matter of time before they break out onto the surface again.

We need to strike at them below ground, and our strategists have devised a new attack plan. It has been added to the Situation Log.

 
Trigger conditions:
  • Subterranean Invasion!
Is triggered only by:

Defeating the invading armies


We need to solve this problem for good.
  • Issue Special Project: Destroy Subterranean Civilization

Defeat


Our forces have been decimated on [colony name], and the subterranean aliens have taken full control over all of our settlements! They are using one of our own satellites to send a message to us.

 
Trigger conditions:
  • Subterranean Invasion!
Is triggered only by:

Failing to defend the colony


On screen.
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