The Precursors are long dead galactic empires predating even the fallen empires and the curators. Their ruins are scattered across the galaxy for the player to find via anomalies or archaeology sites. Precursor anomalies grant a special project which once investigated grants a small amount of Engineering, Physics or Society research as well as a precursor artifact. 6 artifacts are required to reveal the location of a precursor's home system.
If every precursor anomaly has been investigated but no empire managed to collect 6 artifacts a random event can trigger every 20 years and add another precursor anomaly on one of the previously investigated planets. The time is lowered to 13.3 years for Gestalt Consciousness empires.
AI empires can also sell a discovered artifact to Player empires for 1000 Energy. If the Player empire has the Warrior Culture civic it can threaten the AI empire to surrender it for free, the success rate depending entirely on both empires' Relative Power. Empires that hold a Protective, Friendly or Loyal attitude will offer the artifact for free instead of asking for payment. Each AI Empire will only offer an artifact once.
Once a Precursor homeworld has been discovered the empire will gain an artifact action to spend 50 Minor Artifacts to start a special project to delve into the secrets of one of the Precursor civilization. Finishing the special project will grant a permanent empire benefit. If the DLC is installed precursor anomalies will also grant 1-5 Minor Artifacts.
Archaeological Sites are areas where remains of ancient civilizations have been preserved relatively intact. That can be discovered on survey, generated at game start or discovered a few years after a planet is colonized. Each time a planet is surveyed there is a 1.25% chance of an archaeology site being discovered.
A site can have 1-6 Chapters in addition to an introduction Chapter. Each Chapter has its own narrative and rewards and has to be unlocked before it becomes visible. Chapters are unlocked via Excavation. As long as an Archaeological Site is within an empire's borders that empire can task a Science Ship to excavate the site. The duration of an Excavation is determined by the Archaeological Site's Difficulty rating and can be reduced by -25% if the Scientist on the Science Ship has the Archaeologist trait. As the Scientist goes through excavations, it will generate a random number from 1 to 10 and add modifiers to the result, with the following formula:
Result = dice roll + archaeology skill + clues − difficulty. Additional events can also trigger at the end of each excavation.
The On the Shoulders of Giants Origin adds a lengthy Archaeological Site chain in the empire home system. The narration of the last two chapters of the final site are random but the rewards are always the same.
Site
Chapter 1 rewards
Chapter 2 rewards
Chapter 3 rewards
Chapter 4 rewards
Ex Gravitas
1-5 Minor artifacts
1-5 Minor artifacts
1-5 Minor artifacts
100-500 Minerals
Something Waiting site location
Something Waiting
1-5 Minor artifacts
1-5 Minor artifacts
1-5 Minor artifacts
1-5 Minor artifacts
Random Technology
Buried Deep site location
Buried Deep
1-5 Minor artifacts
1-5 Minor artifacts
Random Technology
In Memoriam site location
In Memoriam
1-5 Minor artifacts
1-5 Minor artifacts
1-5 Minor artifacts
1-5 Minor artifacts
Random Technology
The Last Stand site location
The Last Stand
1-5 Minor artifacts
1-5 Minor artifacts
1-5 Minor artifacts
Random Technology
1-5 Minor artifacts
Dark Secret site location
Dark Secret
1-5 Minor artifacts
1-5 Minor artifacts
350-2000 Minerals
250-1500 Alloys
250-1500 Exotic Gases
1-5 Minor artifacts
1-5 Minor artifacts
Spurred by the Past empire modifier
Once the Mid-Game year is reached an event chain will trigger
Precursor Archaeology Sites are visible only to the empire that starts the event chain and are used to advance the Baol and Zroni event chains. When a Zroni Archaeology Site is discovered the planet will gain a deposit of 2-4 Zro.
Precursor
Site
Chapter 1 rewards
Chapter 2 rewards
Chapter 3 rewards
Chapter 4 rewards
Chapter 5 rewards
Baol
Grunur Ruins
5 Minor artifacts
5 Minor artifacts
The Barren site location
The Barren
5 Minor artifacts
5 Minor artifacts
5 Minor artifacts
The Shattered site location
The Shattered
5 Minor artifacts
5 Minor artifacts
5 Minor artifacts
5 Minor artifacts
The Silenced site location
The Silenced
5 Minor artifacts
6-10 Minor artifacts
Grunur system location
Zroni
Abandoned Colony Ruins
1-5 Minor artifacts
1-5 Minor artifacts
90-250 Physics research
1-5 Minor artifacts
150-500 Society research
Psionic Theory technology unlocked if not Gestalt Consciousness
The Sentinels is an Archaeology Site with slightly different mechanics. It can be discovered after a planet is colonized and unlike all others it brings a choice when completely excavated. When discovered it adds an Archaeological Site blocker to the colony.
Chapter 1
Chapter 2
Chapter 3
Difficulty
2
2
3
Rewards
1-5 Minor Artifacts
1-5 Minor Artifacts
1-5 Minor Artifacts Archaeological Site blocker removed
When the site is completely excavated the empire will get the following choices:
If not Xenophobe or Fanatic Xenophobe gain an Unity from Jobs planet modifier and a permanent blocker.
If not Xenophobe or Fanatic Xenophobe issue a special project to open the Sentinels. When the special project is complete the empire will have the option the hear the Sentinels or attack. Attacking will have the Sentinels invade the colony with 9 armies. Hearing them out will bring the option to either gain a permanent blocker and 9 defense armies or be hostile and have the Sentinels invade the colony with 9 armies. The invasion has an Army Strength of roughly 2400.
Issue a special project to destroy the Sentinels. When the special project is complete the will be invaded by 9 armies. If the armies are defeated the colony will gain the Sentinels planetary feature and empire will be offered to either gain 150 Influence or issue a special project to see what the Sentinels were guarding. Finishing the special project will bring the following options:
Gain 300 Influence and the Cheap Thrills planet modifier that gives -10% PoP Consumer Goods Upkeep and a +5% Happiness.
Gain the The Evermore planet modifier that gives +10% Research.
Gain access to the Replicate the Evermore special project.
If Militarist or Xenophobe gain 300 Influence and access to Cheap Thrills planet modifier that gives +10% Militarist Ethics Attraction, +10% Xenophobe Ethics Attraction, -10% Consumer Goods Upkeep and +5% Happiness.
Assuming you never get any of the aforementioned events, the average number of rolls required to complete the chapter can be read from this table. "S + C - D" is the scientist's archeology skill, plus clues, minus difficulty. A level 3 scientist with Curator Archaeology Lab tech researched and 2 clues, excavating a level 4 chapter, would have an S + C - D of 5 + 2 - 4 = 3, and will need slightly under four and a half more rolls, on average, to complete the chapter.