Fortresses

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.