Territories are the smallest unit of land in Imperator: Rome, and they are the basic unit of territorial organization for most ingame mechanics, such as territorial ownership, pops with their associated output, culture, and religion, army movement, occupation, and recruitment, and more. Every province belongs to a particular province, which themselves are grouped into regions.
- 1 Mechanics
- 2 Territory rank
- 3 Country capital
- 4 Provincial capital
- 5 Terrain
- 6 Supply limit
- 7 Civilization value
- 8 Uncolonizable territories
Most territories can have an owner and be colonized, or not be owned by any country at all; unowned territories are considered uncolonized. Uncolonized territories are not necessarily uninhabited and can be colonized by neighbouring countries to directly take ownership of them. Ownership is not to be confused with having control over a territory, which is typically the owner but can also be an enemy occupier during times of war. Certain territories are uncolonizeable and cannot be properly owned or have a population; they may be merely uninhabitable but still accessible by armies or consist of completely impassable terrain. Separately, there are also sea territories, including major rivers, that cannot be owned and are inaccessible by armies, but can be traversed by ships.
All pops live in a certain territory, and they are the source of nearly every resource that a territory produces. A territory's population is limited by the territory's population capacity, which gives scaling penalties if exceeded, and the demographic makeup of a territory's pops determines its dominant culture and dominant religion. The owner of the territory, if there is one, determines who the pop's output is paid towards and what modifiers affect their happiness, which produces unrest if too low and in turn affects province loyalty. Pops can migrate from territory to territory of their own accord, with pops moving from territories of low to high migration attraction, and certain pop types - slaves, as well as tribesmen for tribal countries - can be instantly moved in and out of owned territories by the state at the cost of gold. It is possible for a territory to lose all its population to war or migration, which will automatically make it uncolonized if it is owned.
Each territory has a specific terrain type that affects food production, population capacity, movement cost, combat dice rolls, and more. Rivers, including major rivers, cross between and through many territories and also give a significant modifier. Certain coastal territories are marked as ports, enabling them to build and service ships. All terrain features are set at the beginning of the game and cannot be changed.
Cohorts are recruited and ships built from individual territories, with the buildable types depending on the trade roots that the territory's province has access to. Every army and navy is always located in a particular territory, and can perform unit actions that may have specific effects on the territory that it is present in. Armies and navies can always move into neighbouring territories, as long as they have access; certain territories that are not actually adjacent but separated only by a narrow body of water may be considered connected across the strait.
Every territory has a certain type of trade good that is produced there, with the exact amount depending on the number of slaves compared to the slaves needed for local surplus' as well as any base resource production modifiers. The trade good of a territory is normally constant, but can be changed through certain actions and events.
A territory can have one of three ranks - settlement, city, and metropolis - which determines its population capacity and pop class ratios, and indirectly the main types of output that its population will produce. A country can invest gold and political power to upgrade a territory's rank, or spend tyranny to tear a city or metropolis down.
Depending on its territory rank, territories can have a number of buildings built in them that grant various modifiers and bonuses, particularly for increasing pop output and happiness as well as modifying the pop ratio. While settlements can only have on building built, cities and metropolises can have multiple buildings, capped by the territory's number of city building slots. Buildings can also provide fort level, which create a zone of control over the surrounding territories and make it so that the territory needs to be sieged down before it can be occupied by hostile armies.
In addition to buildings, territories can be connected by roads, which significantly increases army movement speed, and hold holy sites honouring a certain deity, improving the territory's economy and enhancing the deity's bonuses if it is worshipped in the owner's pantheon. Every territory, except for country capitals, has a holding slot that may be granted or acquired by heads of family to increase their power and wealth, though they may also invest in their owned territories.
Every province has a single territory designated as its province capital; similarly, every country that owns at least 1 territory has a country capital. These capital territories get various bonuses and are important to control during wars, and can be moved around within the province or country to larger cities or more defensible locations.
Territories can also have territory modifiers that grant various bonuses and maluses to the territory and the pops that live in them. Certain special modifiers are permanently placed in certain territories at the beginning of the game, and cannot be gained or lost.
Every territory has a civilization value, representing the overall level of development and how settled the territory is, which impacts pop happiness, population capacity, and supply limit. Other territory modifiers and values include food, which is produced in a territory according to its terrain type and consumed by pops in the province; supply limit, which determines how large of an army a territory can support before it starts to take attrition; and barbarian power, which determines the rate at which barbarian hordes will rise up from barbarian strongholds in impassable terrain.
Finally, every territory always has the following base modifiers:
- +0.01% Monthly Civilization Change
- +10 Population Capacity
- +1 Migration Attraction
- +0.04% Local Population Growth
- +100 Provincial Food Capacity
Every territory has a certain territory rank that broadly determines its economic role and general level of development. Each rank has a certain associated modifier that is the main determinant of a territory's population capacity and pop class ratio, as well as the buildings that are available to develop and specialize the territory. Every additional rank also grants an extra altar to any holy sites in the territory, allowing it to hold one more treasure.
A territory's rank generally does not change unless it is specifically modified by certain actions or events, and will retain its rank even if it is completely depopulated and then recolonized.
Settlements represent more sparsely populated rural areas, typically with a heavy focus on agriculture and other primary production and comprising the vast majority of territories in the game. In monarchies and republics, they have a base population ratio of 20% freemen and 80% slaves, while tribal settlements have a base ratio of 50% tribesmen and 50% slaves, which means that they are generally the main source of trade goods and food in a province, as well as producing a significant portion of a country's tax income and manpower. Every settlement has the following modifiers:
- +5 Population Capacity
- -5 Slaves needed for Local Surplus
- -25% Population Output
- -25% Pop Promotion Speed
- -3 Migration Attraction
- -75% Migration Speed
Settlements can only ever have one building slot, but have their own unique set of powerful buildings that can be used to specialize settlements towards manpower, trade good production, or tax income.
Cities represent urbanized areas that have been granted city status, historically often a set of special civic privileges and political autonomy granted to a particular urban community that would become the commercial and political center of the area. Cities have a significantly higher population capacity than settlements and more importantly can sustain significant populations of nobles and citizens, which makes cities the main source of trade routes and research points. Cities have a bonus to Base Resource Production, but the lower proportion of slaves and higher surplus threshold means that cities are not especially efficient at producing trade goods (though very large cities will still end up accumulating enough slaves to produce a significant amount of surplus trade goods). More importantly, the large population and significant proportion of higher pop classes means that cities will have significant food consumption, which in some cases will require the import of food trade goods to sustain. Unlike settlements, cities can have multiple building slots, with the exact amount depending on the city's population and many other modifiers. Cities can be easily distinguished on the map as a group of buildings in the the territory, which shrinks and grows with the actual population of the city. At the start of the game, many cities large and small are found all across the civilized world, from the shores of the Mediterranean through the ancient cities of the Middle East and the great centres of Central Asia and India.
- +20 Population Capacity
- +2 City Building Slots
- +1 Base Resource Production
- +30% Local Citizen Desired Ratio
- +40% Local Freeman Desired Ratio
- +15% Local Noble Desired Ratio
- +15% Local Slave Desired Ratio
New cities can be founded from owned settlements at any time, allowing countries to slowly shape and develop the world according to its desires and reflecting the great city-building empires of the era. Founding a city takes 2 years to be complete, during which the settlement will get the City Under Construction modifier, giving -100% Population Output. Any settlement producing an agricultural trade good ( grain, fish, livestock, or vegetables will switch to a new trade good once the city is finished; if city status is subsequently revoked, the trade good produced in the territory will revert to the old food trade good. While granting city status will not have any immediate impact on the population, the significantly higher migration attraction of cities means that pops in the surrounding territories will slowly migrate to nearby cities, particularly if it is also the province capital. Enslaving pops during wars can also be a good method of filling up cities with pops.
- -25% with Etruscan, Heraclean, and Zipoetic (Bithynian) heritage
- -20% with Rural heritage
- -15% with Ptolemaic (Egyptian) heritage
- -10% with the Household Gods invention ( Religious Advances 14)
- +25% for Tribal countries
- +50% with the Nomadic Lifestyle Tribal law
It is also possible to revoke city status from a city as long as no construction or other upgrades are ongoing in the territory, whether to centralize the population more effectively, force the demotion of unwanted nobles and citizens, or even simply as an act of spite. Revoking city status costs a base of 5 tyranny, modified by the Revoke City Status Cost modifier (with -50% for tribal governments as the only source), which will instantly downgrade the city back to a settlement and give the Revoked City Status modifier for 5 years, giving -10% Local Population Happiness and -2 Migration Attraction as well as preventing city status from being granted back as long as the modifier exists. The significant decrease in population capacity will usually put the territory well over the limit, which will quickly decrease the population by emigration and pop death.
A metropolis is considered the peak of a city’s urban evolution and can only be made from the very largest cities of a region. Metropolises do not have any special mechanics that set them apart from cities, but instead have generally stronger modifiers that allows it to support an even larger and more productive population, making them advantageous to construct in a country's largest cities, particularly the by the mid to late game. The only metropolis that exists at the start of the game is the Mauryan capital of Pataliputra.
- +30 Population Capacity
- +10% Population Capacity
- +4 City Building Slots
- +1 Local Import Routes
- +2 Base Resource Production
- +10% Pop Promotion Speed
- +2 Migration Attraction
- +30% Local Citizen Desired Ratio
- +30% Local Freeman Desired Ratio
- +10% Local Noble Desired Ratio
- +5% Local Slave Desired Ratio
Note that a city that has been upgraded to a metropolis is still considered to have city status.
A metropolis can be founded on an existing city that has at least 80 population and is the province capital. Founding a metropolis costs a base of 400 gold and 100 political influence; like cities, the process takes 2 years to complete during which the settlement will get the Metropolis Under Construction modifier giving -100% Population Output. It is possible to have multiple metropolises in a single province by simply moving the province capital to another city and building a new metropolis there; this will not destroy the previously existing one.
Like with cities, it is possible to revoke city status from a metropolis, which will downgrade the territory all the way back to a settlement. Revoking city status from a metropolis costs a base of 10 tyranny, modified by the Revoke Metropolis Status Cost modifier (with -50% for tribal governments as the only source) and has the same effects as revoking city status from a city.
Every country that owns at least one territory has a capital territory, the seat of the government and usually the largest, wealthiest, and most important city in the country. The capital territory gets the following modifiers:
- +10% Supply Limit
- +0.02% Monthly Civilization Change
- +10% Population Output
- +10% Local Noble Desired Ratio
- +4% Local Citizen Desired Ratio
- +4% Local Freeman Desired Ratio
- +8% Local Noble Happiness
- +8% Local Citizen Happiness
- +10 Population Capacity
- +1 City Building Slots
- +25% Pop Promotion Speed
- +2 Migration Attraction
- +20% Pop Conversion Speed
- +20% Pop Assimilation Speed
- +1.50 Local Monthly Food
In addition to these baseline bonuses, the capital territory is also often granted permanent bonuses by a number of decisions and missions, most notably all country formation decisions and the generic infrastructure mission. This makes it advantageous to make the capital as large as possible, as pops in the capital are usually far more productive than pops in any other territory and usually have the highest citizen and especially noble ratio given the combined effects of the base capital bonus and the number of buildings that are typically built there due to its high population. By the midgame, the capital territory will often have outgrown its local food supply and begin to necessitate imports food goods to feed its growing population, though the high proportion of noble and citizen pops usually means that the capital has many more import route slots than is needed to feed it.
The province and region that the country capital is also have special modifiers and mechanics that generally make them more valuable than more peripheral areas. Control of a country's capital is important during wars, as it is worth extra warscore and provides bonus war enthusiasm for countries that still control their capitals, as well as being one of the main targets that enslaved pops to be sent to - slaves will generally go disproportionately to the capital territory, unless it has reached its population capacity. The capital is also the point from which diplomatic range is calculated from (for non-neighbouring countries).
If desired, the capital can be moved at any time to a territory of the primary culture and state religion in a loyal province as long as the country is not at war. The cost is 50 + 5 times the difference in population between the current capital and the new capital in political influence, with a minimum cost of 80 and a maximum of 250. This means that it is much cheaper to move the capital to a more populated territory than vice versa.
Every province that a country owns or partially owns has a province capital, representing the center of the local administration. If multiple countries own part of the same province, each part of the province belonging to each country will have its own provincial capital. The capital of the capital province is always the same as the national capital.
Provincial capitals get the following bonuses:
- +10% Population Output
- +6 Population Capacity
- +10% Pop Promotion Speed
- +1 Migration Attraction
- +1 Local Monthly Food
Province capitals are important in wartime as they determine who controls the province as a whole. A province cannot be demanded in a peace treaty unless its capital (as well as all forts) are occupied, and armies can only resupply in foreign territory if the capital of the province is occupied. They are also the primary targets for receiving slaves when occupying enemy territory, after the national capital.
Provincial capitals may be relocated during peace time for a cost of provincial loyalty. Relocating the provincial capital to a settlement lowers provincial loyalty by 30, to a city lowers loyalty by 20, and to a metropolis by 10.
Every territory has a fixed, predefined terrain type that cannot be changed. Terrain type has a significant impact on a territory's habitability through population capacity and food production modifiers, and is important to consider for army maneuvering and supply as well. Generic heritages are also assigned partly based on the terrain type of a country's capital territory at the start of the game.
Sea territories also have terrain types like land territories. The primary effect of sea terrain is to affect the movement speed of ships.
Each territory also has one of five possible climates depending on its geography, which gives an additional smaller modifier to population capacity and food production. Certain climates also have winter for part of the year, which has an effect on attrition.
Warm Climate is the most hospitable type and covers the largest part of the map, from the shores of the Mediterranean to the Fertile Crescent and the rich plains of India. Every territory with Warm Climate gets the following modifiers:
Temperate Climate is common directly to the north of warm areas, such as in Britannia, Gaul, Moesia and Illyria, northern Anatolia, and the south of central Asia. Territories with temperate climate have no default modifiers.
Frigid Climate represents colder areas of the map where harsher winters have a significant effect on habitability, such as in Scandinavia, Germania, and the north of central Asia. Every territory with Frigid Climate gets the following modifiers:
Alpine Climate describes cold mountainous areas, such as Tibet and parts of the Caucascus. Every territory with Alpine Climate gets the following modifiers:
Arid Climate describes desert regions and nearby drier areas, such as the areas around the Sahara, parts of the Arabian Peninsula, and much of Persia. Every territory with Arid Climate gets the following modifiers:
Rivers were central to trade and transportation in this time period and the presence of a significant river usually made that area much more attractive to settle in, as well as being more defensible given the inherent difficulties of crossing a river. Ingame, a territory with a Nearby River gets the following modifiers:
- Attackers get a -1 penalty to their dice rolls
- +5% Population Capacity
- +5% Supply Limit
- +10% Pop Migration Speed
Parts of certain very large rivers, such as the Rhine, Danube, Nile, or Indus are considered major rivers, which makes them navigable by ships and crossable only at certain points. Mechanically, major rivers are considered sea tiles for most intents and purposes, with crossing points marked as straits. A territory that is Adjacent to Major River gets the following modifiers:
The population capacity bonus means that territories next to a river, especially a major river, are generally good city sites. Note that if a territory is both adjacent to a major river and has a nearby (minor) river, it will have the effects of both modifiers.
Coastal territories also get small bonuses by virtue of their access to the sea, which like rivers often served to connect areas together even if there was no good port nearby. The following modifiers are given to all coastal territories without a port:
Note that this modifier can potentially stack with both river modifiers, if the territory meets all the requirements.
Certain coastal territories with a particularly good harbour are designated as ports. Ports represent areas that are particularly accessible to ships and naval transport and are placed in certain territories at the beginning of the game, including some that some distance upstream on major rivers, and as a terrain feature are fixed and cannot be built or destroyed during the course of the game. Ports are at the center of a country's navy, as ships can only dock and be built at coastal territories with ports. In addition, every territory with a port gets the following modifier, replacing the modifier for non-port coastal territories:
- +10% Population Capacity
- +5% Supply Limit
- +10% Pop Promotion Speed
- +2 Migration Attraction
- +50% Pop Migration Speed
Like with the standard coastal modifier, port modifiers can potentially stack with both river modifiers, if the territory meets all the requirements. The population capacity, migration attraction, and promotion speed modifiers in particular make port territories good places for founding cities, particularly those that are also adjacent to a major river.
Certain ports are home to pirate havens where groups of pirates are based from. These pirate havens are present in certain ports at the beginning of the game, and in addition to giving an economic boost of +20% Local Tax and +0.01% Local Population Growth to their territory they host pirate fleets, always composed of all light ships, which can rented out as naval mercenaries at times of war. When not being hired pirate fleets will eventually grow restless and go on raids, at which point the fleet while become hostile to all other navies and travel to nearby unfortified ports to plunder them, giving -25% Local Tax and +10% Demotion Speed to the plundered territories.
If pirates grow to be too much of a problem, their havens can be destroyed using the Root Out Pirates army ability on any controlled territory once the anti-pirate law has been passed, including those belonging to other countries that have been occupied in a war. This will remove the modifier (including its beneficial modifiers) and destroy the associated pirate fleet, even if it is currently out on a raid. Alternatively, pirates can be actively encouraged by passing the pro-pirate law, which will create a new pirate haven in one of the country's ports to increase its prosperity and provide more available naval mercenaries at the expense of the nearby coasts.
The supply limit of a territory determines how large of an army it can sustain before the army begins to take attrition, with every point of army weight over the supply limit giving 1 point of attrition. As attrition increases food consumption rather than immediately causing loss of soldiers, being over the supply limit is not particularly problematic as long as the army is just quickly passing through or is adequately supplied with enough food to feed itself, but can become a significant issue with longer campaigns in low supply limit areas.
Generally speaking, more fertile, developed, and highly populated areas have a higher supply limit. All modifiers affecting the supply limit of a territory are listed below (note that national modifiers, e.g. inventions and deities, are based on the owner of the army, not the owner of the territory):
|Population||+0.5 per pop|
|Capital Territory||+10% per point|
|Civilization Value||+2% per point|
|Critical Food Supply||-25%|
|Terrain||Adjacent to Major River||+10%|
|Inventions||Supernumerarii (Military Advances 1)||+10%|
|Fighting Season (Military Advances 4)||+10%|
|Logistics Division (Military Advances 11)||+10%|
|Delayed Baggage Train (Military Advances 15)||+25%|
|Central Reserve (Military Advances 19)||+25%|
|Deities||Armazi (Armazic deity)|
|Kakasbos (Cybelene deity)|
|Pan (Hellenic deity)|
|Diktynna (Cretan Hellenic deity)|
|Turan (Etruscan Hellenic deity)|
|Faunus (Italic Hellenic deity)|
|Medeiné (Matrist deity)|
A territory's civilization value represents its level of infrastructure and urbanization and is the biggest contributors to pop happiness, especially for nobles and citizens. Increasing the current civilization value of the capital to 50 is also one of the main requirements for a tribal nation to reform into a republic or monarchy, and some city buildings also require a minimum civilization level. Most countries, except for migratory tribes, will generally benefit from a higher civilization level in their territories.
A territory's civilization value spans between 0 and 100, with each point granting the following local effects:
- Population Capacity: +0.25%
- Supply Limit: +2%
- Barbarian Growth: -0.005
- Migration Attraction: +0.1
- Local Citizen Happiness: +0.5%
- Local Freemen Happiness: +0.3%
- Local Noble Happiness: +0.7%
- Local Tribesmen Happiness: -0.4%
Maximum civilization level
Each territory has a maximum possible civilization value, which is the sum of its owner's country civilization level and any province or territory-specific modifiers to local civilization level. The country civilization level is generally the most consequential, as it is applied across all the territories in the country, and its value is determined largely by a country's government form, its level of Oratory Advances, and positive centralization for tribal nations. Local modifiers can increase the civilization level of certain territories, particularly the capital, much higher than the country-wide value and is mostly given from decision modifiers (especially when creating formable nations) and coordinating urban development.
All static sources of maximum civilization level are listed below.
|Centralization Level||+0.1% per point above 0% (up to +10% at 100%)|
|Autocratic Monarchy or Democratic Republic||+30%|
|Other Monarchies or Republics||+35%|
|Empire or Imperial Cult||+40%|
|Laws||Rights of Man (Tribal)||+5%|
|Rights of Birth (Tribal)||+5%|
|National ideas||State Religion (Religious)||+5%|
|Technology||Oratory Advances||+2% per Level|
|Trade goods||Gemstones capital surplus||+5%|
|Glass capital bonus||+5%|
|Heritages||Icenian Heritage (Icenia)||+5%|
|Local||Urban Development||+1% per Level|
|Emergent Center of Civilization (from formable nations)||+5%|
|Center of Civilization (from formable nations)||+10%|
|Emergent Capital (from formable nations)||+10%|
|Capital of the Subcontinent (from forming Bharatvarsha)||+10%|
Note that government bonuses are, of course, exclusive to each other.
Maximum civilization level does nothing by itself, but allows the territory's actual civilization level to slowly rise to that level. Each month, the civilization value of every territory that is below its local maximum civilization level will increase by the value of the monthly civilization change modifier, which can be increased with various omens, inventions, governor policies, and other modifiers. If the local maximum civilization level is lower than the territory's current civilization level, it will instead decrease at a fixed rate of -0.10% per month until it reaches the cap again.
|Type||Modifier||Monthly Civilization Change|
|Barbarian power||-0.025% per point|
|National ideas||State Religion (Religious)||+0.02%|
|Inventions||Recording Tradition (Religious Tech 5)||+0.01%|
|Scribae (Religious Tech 20)||+0.01%|
|Laws||Coin Minting Initiative (Tribal)||+0.03%|
|Deities||Upekkha Parami (Buddhist deity)|
|Maponos (Druidic deity)|
|Wisdom of Bhadrabahu (Jain deity)|
|Omens||Pañña Parami (Buddhist deity)|
|Eshmun (Canaanite deity)|
|Attis (Cybelene deity)|
|Gobannus (Druidic deity)|
|Glanis (Alluvian Druidic deity)|
|Asklepios (Hellenic deity)|
|Amaya (Cretan Hellenic deity)|
|Aita (Etruscan Hellenic deity)|
|Goitosyrus (Heptadic deity)|
|Arubani (Khaldic deity)|
|Tannit (Megalithic deity)|
|Guidance of the Moon (Ritualistic deity)|
|Zalmoxis (Zalmoxian deity)|
|Treasures||Tomb of Romulus||+0.03%|
|Heritages||Etruscan Heritage (Etruria)||+0.02%|
|Hellenistic Heritage (cultural)||+0.01%|
|Governor||Civilization Effort||+0.005% per 10 finesse of the governor, plus a base of +0.005%|
|Urban development||+0.01% per Level|
|Road Network||+0.001% per outgoing road|
|Razed (unit ability)||-0.01%|
The civilization value of territories with city status can be increased above and beyond its natural maximum by using the Coordinate Urban Development action, which costs a base of 25 political influence (modified by the Urban Development Cost modifier) and, after 2 years, will give a stackable Urban Development modifier, giving +1% local civilization level and +0.01% monthly civilization change to the city. This action can only be used while the civilization level of the city is below 60, which means that it is primarily useful only in the early game or for tribal nations looking to improve their capital in preparation for reforming into a monarchy or republic.
Certain particularly harsh or desolate territories are considered uncolonizable. These territories have no true owner or pops and for the most part cannot be interacted with, though they will be considered owned for the purposes of map colouring and naming purposes if there is a single country that owns the majority of the adjacent colonizable territories, as well as owns and/or has coloured in a majority of all adjacent territories, including neighbouring uncolonizable territories. Similar behaviour is used to colour in uncolonizable territories in some other mapmodes, such as culture, religion, province, and region. This behaviour can be toggled on and off using the Fill in impassable terrain setting.
All uncolonizable territories have a culture, religion, civilization value, barbarian power value, and supply limit, which depending on the type of the the uncolonizable territory may have some gameplay relevance. Whether or not a territory is considered uncolonizable is set at the beginning of the game and cannot be changed.
Uninhabitable territories cannot be owned or colonized, but still allow armies to pass through them. They exist in a number of passes through many arid and desert areas, such as in the Arabian pennisula and Central Asia. There are no special penalties for armies marching through uninhabitable territories beyond their low supply limit and inability to replenish food supply. Unlike impassable terrain, uninhabitable territories have a terrain type that helps to determine its supply limit.
All uninhabitable territories also have a culture and religion that is set at the beginning of the game, appears on the relevant mapmodes, and cannot be changed, though this is purely cosmetic and does not have any gameplay effect.
- See also: Barbarians
Impassable terrain represents the harshest and most accessible areas of the map, and in addition to being uncolonizable also cannot be passed by armies and cannot be interacted with directly. Many exist as mountain ranges, inaccessible jungles, or unforgiving deserts crossing through even relatively developed areas, serving to isolate certain areas from one another and represent the difficulties that these types of terrain posed for states trying to exert their control across them.
Certain areas of impassable terrain hold barbarian strongholds, from which barbarian hordes will occasionally rise up to pillage and settle neighbouring territories. These barbarian strongholds can be particularly dangerous and require some military investment to control and hold off, but can eventually be pacified by raising the stronghold's civilization value high enough using the Civilization Effort governor policy in a neighbouring province.
Impassable terrain has a culture and religion that is used when generating barbarian hordes that rise up from that territory. However, in the culture and religion mapmodes the colour of impassable terrain will instead be determined by the majority colour of the surrounding territories according to the same rules as colouring for ownership, which may be different from the actual culture or religion of the territory.