Fortresses are a feature introduced in the Tempest expansion, which adds a great deal of complexity towards the naval aspect of the game. The oceans of Auriga are divided into various oceanic regions, and these regions may be host to one to three Fortresses - large structures that rise from the depths that can act as safe havens on the seas for those who control them, as well as providing access to resources and special facilities.
At the start of the game, all fortresses are held by Fomorians, who can be seen as the naval equivalent to neutral Minor Faction villages. A few neutral naval units will be garrisoned in each fortress, starting with Boarding Vessels at the start of the game, and moving up to Artillery Ships as the game progresses. Additionally, these neutral fortresses will create roaming naval armies that patrol the oceans and will attack any non-Fomorian armies they can. This can make traveling through neutral oceans very dangerous for Transport Ships, as even low-level Boarding Vessels will have no trouble defeating them in battle, and so makes capturing oceans a high priority on maps that require a lot of water travel, if only to make the oceans safer for embarked units.
Capturing Fortresses[]
As stated before, at the start of the game, all Fortresses are controlled by the neutral Fomorians. However, control can be wrested from them in two ways. The first is to simply attack the fortress and destroy all units garrisoned in it. Doing so will grant you control of the fortress immediately. However, it should be noted that any roaming neutral armies in the area will immediately move to reclaim it, so you should either make sure all the roaming armies in the ocean have been defeated, or have your units wait for them to show up and defend your new acquisition.
The second method is by talking to the fortress, initiating a Naval Quest. Upon completion of the quest, control of the fortress that issued the quest will be given to you, though it will not have any units garrisoned in it, making it a prime target for others to conquer, or even for a nearby neutral army to re-capture. If capture a fortress with this method, and then lose it to a neutral army, you cannot re-capture it by doing another quest, and must conquer it by force. Note that this method doesn't require having unlocked the Language Square technology, and so can be performed by any faction from the start of the game.
Upon capturing a fortress, if it is the last or only fortress in the region, you will automatically gain control over the region, indicated by the ocean turning your faction's color. If there are other fortresses in the region you haven't captured yet, they will be revealed on your map if you haven't already seen them. Capturing those fortresses should be a high priority for you, as gaining control over all fortresses in a region - and thus the region itself - comes with a number of benefits.
First, if all the fortresses in a region have been conquered, that means that roaming armies will no longer spawn from the neutral fortresses, and won't be a constant threat to what fortresses in the region you do control. Second, if you don't control all the fortresses in a region, any other empire in game you are not at peace or in an alliance with can attack your fortress, and potentially gain control of it themselves if they beat your garrisoned units, but if you control the region, then other empires cannot attack your fortresses without declaring war first. Finally, the benefits from the various facilities fortresses have are usually increased by controlling the region.
Fortress Structure[]
Fortresses are divided into two main parts: the Citadel and its adjacent Facilities. The Citadel forms the central part of the fortress, occupying a tile in the ocean, and is where the units garrisoned on a fortress are located. Citadels come in three different forms, each providing a slightly different output of Dust 
, Science 
, and/or Influence 
, as well as bonus Experience and Health Regen 
to units garrisoned in them.
Facilities are attached to the citadel on adjacent tiles. Facilities generally also provides some Dust , Science , or Influence , but can also provide a much wider variety of benefits. The most common type are Strategic Resource and Luxury Resource facilities, which effectively act as extractors for the given resource, though you don't need the associated technology to gain the resources from the facility, making them one of the quickest ways to get a steady supply of the more advanced resources. There are also a number of unique facilities that only appear once in the world, but provide a variety of special bonuses, many of which become stronger the more fortresses you control. It should be noted that many of the types of facilities in the game only become active in later technological eras, and are useless "Unrevealed Facilities" up until that point; however, such facilities become revealed the turn that any empire in the game reaches the requisite era, so you do not necessarily need to be in Era IV to have a facility that is only revealed then, so long as some other empire in the game has reached Era IV.
Fortresses will always have a Citadel, and typically have one to three adjacent Facilities, though it is possible for a fortress to have no facilities.
Citadels[]
Bastion
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This citadel is the epicenter of the Fortress, where the faction lives and trades are done. | ||||
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Effects:
+1 | ||||||
Listening Post
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This tower is specialized in looking and listening for distant events that affect the area around the Fortress. | ||||
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Effects:
+1 | ||||||
Manufactorium
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A key part of trade and commerce, the Manufactorium produces useful goods for the Fortress. | ||||
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Effects:
+1 | ||||||
Facilities[]
Unrevealed Facility
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Facilities are platforms providing bonuses and resources exploitation. Facilities like this have not yet opened to show what they are hiding. | ||||
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Effects:
None | ||||||
Strategic Resource Facility
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Facilities, like this one that mines [Strategic Resource], are platforms that provide bonuses and resource exploitation. You can never know how much will be exploited by the fortress. | ||||||
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Effects:
+1 | ||||||||
Luxury Resource Facility
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Facilities, like this one that mines [Luxury Resource], are platforms that provide bonuses and resource exploitation. You can never know how much will be exploited by the fortress. | ||||||
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Effects:
+1 | ||||||||
Food Stockpile Facility
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Under a strange dome with almost invisible doors, a vast area is kept cool and dry by some magical means. | ||||||
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Effects:
Regularly generates a Food Stockpile | ||||||||
Industry Stockpile Facility
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A vast warehouse for storing parts, raw materials, and partially assembled machines is now at your disposal. | ||||||
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Effects:
Regularly generates an Industry Stockpile | ||||||||
Vision Facility
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Spires of glass and metal extend, like living antennae, and on magical screens the garrison can see images of distant areas. | ||||||
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Effects:
+2 Vision | ||||||||
Science Stockpile Facility
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A veritable warehouse of ideas, samples, experimental results, and careful documentation, this facility is designed to hoard scientific knowledge. | ||||||
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Effects:
Regularly generates a Science Stockpile | ||||||||
Strategic Boost Facility
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Full of furnace models, designs of mining tools and machines, and explanations of transport processes, the ideas in this facility will greatly improve the production of strategic resources. | ||||||
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Effects:
+50% Strategic Resource ( | ||||||||
Luxury Boost Facility
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Explanations, tools, and machines that aid in harvesting, crafting, refining, setting, polishing, and distilling guarantee improved luxury production. | ||||||
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Effects:
+50% Luxury Resource ( | ||||||||
Cargo Nexus Facility
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With magically automated docks, cranes, and slipways,this facility will greatly increase the volume and value of trade. | ||||||
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Effects:
+5% Trade Route Bonus on Cities from Cargo Nexus Facility | ||||||||
Center of Influence Facility
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This facility disgorges a time-worn statue striking in its color and splendor; travelers come from far and wide to marvel at it - and the empire that owns it. | ||||||
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Effects:
+2% | ||||||||
Naval Architecture Facility
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Full of designs and instructions for procedures for shipbuilding, the opening of this facility will greatly increase the efficiency of ship production. | ||||||
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Effects:
+10% Naval Unit Production Cost Reduction on Cities from Naval Architecture Facility | ||||||||
Component Design Facility
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The clever modules and assemblies in this factory will aid in optimizing the use of space and materials in ship construction. | ||||||
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Effects:
+10% Attack | ||||||||
Dust Accumulator Facility
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This special facility aids in accumulating Dust. Facilities are like platforms providing unpredictable bonuses and resource exploitation. | ||||||
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Effects:
+2% | ||||||||
Vile Tide Facility
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This series of gardens and ponds, meant for the study of algae, fortunately creates forms of plankton that are repellent to monstrous sea creatures. | ||||
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Effects:
Prevents the Fleets from being attacked by the Sea Monster | ||||||
Sky-Shaker Facility
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When activated, the air and water tremble as great waves and winds affect the seas, the temperature, and the atmosphere. | ||||||
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Effects:
Gives the ability to deregulate the Weather on Sea Tiles | ||||||||
