The population of the world in Imperator Rome is represented by individual "population units", or “pop” for short. Each population unit has a unique ID in the save game file.
A pop belongs to one of the five available social classes. The social class of a pop is one of its most important properties and determines what a pop produces, its political weight, what happiness modifiers it is affected by, and more.
- Nobles - generate research points and trade routes
- Citizens – generate research points, trade routes and manpower
- Freemen – generate manpower and tax income
- Tribesmen – generate manpower and tax income
- Slaves – generate tax income and additional trade goods
The class structure of a territory's population will approach its optimal ratio over time through pop promotion and demotion, the value of which is specific to each territory and varies by the territory's buildings and rank, the country's government form, local and national modifiers, and many other factors. This ratio and the rate of change can be affected by player choices, and promotion is additionally restricted by the pop's level of civic rights based on its culture.
There are also a few other effects that can directly change a pop's social class:
- When a territory is occupied, there is a chance that some pops will be immediately demoted one level: Nobles ⇒ Citizens (5% chance), Citizens ⇒ Freemen (25% chance), and Freemen ⇒ Slaves (25% chance).
- When any territory is occupied, some of its pops will be enslaved according to the army's enslavement efficiency and immediately moved to one of the occupier's territories, usually a provincial or country capital, as a new slave pop (keeping its culture and religion).
- Some events can also immediately promote or demote pops.
Nobles also have the following other properties:
- 300% Political Weight
- 0.5 Food Consumption
- -50% Base Happiness
- +0.40 Base Assimilation
- +0.40 Base Conversion
- +1 Base Demotion Speed
- +1 Base Migration Speed
Nobles only have a relevant desired Ratio in cities, metropolises, and the capital (even if it does not have city status). Their happiness is heavily affected by civilisation level and is in general difficult but important to manage, with both the lowest base happiness and the highest political weight of all pop classes. Both their ratio and happiness can be increased via the library, while the academy increases their ratio by half as much along with their (significant) research output.
Nobles are generally the most powerful and productive pop type and it can be advantageous to maximize the number of nobles in the country, as long as their happiness can be kept under control - their high food consumption is significant, particularly in the capital where they are concentrated in large numbers and will often outstrip the local food supply, and their low happiness and high political weight makes them dangerous if not properly appeased. Trade goods are an important source of happiness modifiers, and as they are applied-province wide it is usually best to focus most on noble ratio in cities in the capital province (which has the additional benefit of usually being primarily the primary culture).
Noble civic rights are rather exclusive, giving a combined -4% Integrated Culture Happiness malus and -5% Primary Culture Happiness for every non-primary culture, which means that granting these rights give a heavy penalty and generally only primary culture pops will have the civic right and be able to promote to nobles. However, conquered noble pops will in general remain in significant numbers and non-integrated culture noble pops can be a significant source of unrest when conquering the cities and especially capital provinces of other countries, and will additionally be slow to assimilate, convert, and demote, ensuring that they can be a persistent problem.
Citizens also have the following other properties:
- 150% Political Weight
- 0.3 Food Consumption
- -34% Base Happiness
- +0.60 Base Assimilation
- +0.60 Base Conversion
- +3 Base Promotion Speed
- +2 Base Demotion Speed
- +1 Base Migration Speed
Citizens only have a relevant desired ratio in cities, metropolises, and the capital (even if it does not have city status). Both their ratio and happiness can be increased by the court of law. Citizen civic rights are associated with integrated cultures, and only integrated culture pops will be able to promote to citizens, which can prove to be an obstacle to gaining more citizens in cities with a high non-integrated culture population.
In general, citizens can be considered a weaker form of nobles - less production per pop, but easier to feed, please, and promote to, with a higher desired ratio and a less expensive civic right. In most cities they will still make up a significant form of the population, and can be useful to focus on in cities dominated by integrated cultures that have not been given the full noble civic right.
Freemen also have the following other properties:
- 100% Political Weight
- 0.2 Food Consumption
- -20% Base Happiness
- +0.60 Base Assimilation
- +0.60 Base Conversion
- +4 Base Promotion Speed
- +5 Base Demotion Speed
- +2 Base Migration Speed
Freemen are found primarily in cities, but also have a significant base optimal ratio (20%) in the settlements of monarchies and republics. They are somewhat easier to maintain than citizens, but about equally affected by civilisation level. While freemen produce some tax their primary contribution is as main source of manpower, so their usefulness is highly situational depending on how much additional manpower is needed (mostly medium-size countries that have enough pops to make a significant difference, while not being so large that additional manpower is not really needed). Both their ratio and happiness can be increased via the forum in cities and metropolises, and barracks in settlements, and as the default civic right in non-integrated cultures they will tend to be disproportionate represented in those areas.
Tribesmen also have the following other properties:
- 75% Political Weight
- 0.2 Food Consumption
- 16% Base Happiness
- +0.40 Base Assimilation
- +0.40 Base Conversion
- +1 Base Promotion Speed
- +1 Base Demotion Speed
- +3 Base Migration Speed
Tribesmen have a relatively high base happiness, but unlike all other pop classes receive a penalty for Civilisation level. Their production is comparable to freemen, with a focus on manpower and some amount of tax income, though actually getting those outputs is generally easier with their higher base happiness. In settlements, tribesmen output and happiness can be increased by building Tribal Settlements.
For tribal nations, they make up 50% of the Settlement Population, limiting the space available for slaves and thus trade goods and tax production. In any cities, they are less common, but still have a noticeable ratio. Tribesmen will therefore usually make up a large proportion of a tribal country's population, increasing their manpower relative to what would be expected from their population but usually with less income. Tribesmen also have a high base migration speed which means that they will move around significantly more quickly than other pop types.
For non-tribal nations, while they are technically superior to freemen the significant happiness penalties from civilization value means that tribesmen are usually much better off be promoted or demoted to one of the other classes. For these nations, they have a desired ratio of 0% at any location unless a Tribal Settlement is built, though their slow promotion/demotion speed means that tribesman-heavy territories will usually take some time to become properly useful.
Each Slave Pop produces per month:
Slaves also have the following other properties:
- 35% Political Weight
- -30% Base Happiness
- 0.1 Food Consumption
- +0.60 Base Assimilation
- +0.60 Base Conversion
- +4 Base Promotion Speed
- +0.05 Base Migration Speed
Slaves are the backbone of almost every economy during the time frame of the game and the primary source of income for many countries. There is no nation or territory that does not have, want or need slaves. They are mostly found in settlements, where they have a base optimal ratio of 80% (monarchy/republic) or 50% (tribal) of the population, but are also found in significant proportions in cities. Their happiness, output and desired ratio can all be increased by the mill in territories with city status, and output by the slave estate in settlements. While slaves can appear through demotion and population growth like all other pop types, slaves can also uniquely be acquired through the enslavement of pops when occupying enemy territories, as well as through slave raiding for countries with the relevant military traditions. For many war-focused countries, enslavement can be the primary source of population growth in a nation's core territories, with slaves eventually assimilating/converting and promoting up to swell the ranks of the upper classes as well.
In addition to producing more tax income than any other pop type, slaves can also uniquely produce additional trade goods in a territory, based on the slaves needed for local surplus value of the territory. This value is a base of 15 in settlements and 20 in cities and metropolises, which can be lowered by the mine and farming settlement buildings in (as well as a large variety of other modifiers), and gives 1 extra trade good for every multiple (rounded down) of the slaves needed for local surplus in slaves there are in that territory.
Their happiness can be difficult to keep high, as those captured in war tend to be of the wrong culture and religion. Importantly, however, the output of slaves does not depend on their happiness, which means that the primary concern of slave happiness is controlling the unrest they produce, which given their low political weight is typically not too high.
Depending on their type, pops produce gold, manpower, and research points, and are the main (or only) source of these resources in the game. In addition to the output modifiers for each specific resource, the population output modifier will also increase the production of all resources produced by pops, and is in general one of the most powerful economic modifiers. Pop output can also be affected on a class-specific basis with the local/national noble output, local/national citizen output, local/national freeman output, local/national tribesman output, and local/national slave output modifiers.
Output modifiers are given from a large variety of sources, such as buildings, deities and omens, laws and government forms, inventions, and more. Notably, population output is also significantly decreased by low pop happiness (slaves being the only exception) and high local unrest, which means that keeping pops happy and content is important for maintaining a strong economy.
Output efficiency factors summed up and then applied multiplicative to the base output of each social class. Output efficiency is the sum of:
- Happiness of class
- Code of Rights (freemen) +2.5%
- Right to be Heard (citizen) +5%
- Tyranny: (slaves)+0.5*Tyranny Score
- some trade goods surplus in province (hemp: +2% for slaves)
- Province policies (Harsh Treatment -32% (scales ??), Local Autonomy -60%)
- (Province Investments: reduction for 2 years, needs verification)
- (Province Procurator investment +4%, needs verification)
- Capital Region +10% all classes
- Capital Province +10% all classes
- Capital Territory+10% all classes
- Dominant culture is not primary culture -20% (all classes)
- Settlement -25%
- Religion: Mercury +10%
- Governor Traits (Harsh: slave output +10%)
- Governor Bonus 2.5% per finesse point, (needs verification)
- Foundry +1%
- Harsh Taxation: national slave output +10%
Happiness represents how content and satisfied a particular pop is with the current government, affecting both how much of its production actually gets collected by the state as well as how willing the pop is to support resistance - or even rebellion - against the current government. Each of the five pop types has a certain base happiness value, varying from -50% for nobles to 16% for tribesmen. Then, there are a large number of local and national happiness modifiers that are applied, including but not limited to:
In general, there are 4 different sets of modifiers that will each affect a different set of pops:
- General happiness modifiers ( (Local) Population Happiness)
- Pop class modifiers ( Noble Happiness, Citizen Happiness, Freeman Happiness, Tribesman Happiness, and Slave Happiness modifiers)
- Each of these modifiers has three variants: Local Happiness, applied to a single territory or province; Culture Happiness, applied to pops of a particular culture; and National Happiness, applied to all pops of the specific class across the whole country
- Culture modifiers ( Culture Happiness, Integrated Culture Happiness, Unintegrated Culture Happiness, and Unintegrated Culture Group Happiness modifiers)
- Religion modifiers ( State Religion Happiness and state religion pantheon deity modifiers)
A pop's happiness is the sum of all happiness modifiers it is affected by over its base happiness value, and has a range of 0% to 100%, with 50% the median value at which they are neither content nor discontent. The average happiness of all pops of a particular class is displayed in the territory view.
Happiness has two main effects on a pop:
- Output: a pop's output (except for slaves) is scaled according its current happiness, before other modifiers are applied. For instance, a freeman pop at 50% happiness generates a base of only 1.5 Manpower instead of 3.
- Unrest: any pop with happiness less than 50% will generate unrest in the territory it currently resides in, scaled by its happiness and political weight, which acts as a multiplier on how much unrest it produces - for instance, an angry noble pop will produce far more unrest than a discontent slave. High unrest will lower province loyalty and may eventually lead to rebellions.
The unrest produced by each unhappy pop is scaled to the total population of the territory, the pop's political weight, and how much its happiness is below 50%, giving a formula of approximately:
The total unrest for each territory is simply the sum of the unrest produced over all its pops.
As with all modifiers, national modifiers are almost always better than local modifiers, even if the value is somewhat weaker. Even relatively small changes in happiness can have a noticeable impact on pop output or unrest generated if applied across a large enough number of pops.
Generally, the largest differences in overall population happiness are between integrated cultures and unintegrated, especially unintegrated culture group, pops, with different strategies relevant in each area. While there can be significant differences in pop class happiness, these are usually not too relevant as, for instance, slaves do not have an output difference from happiness and have a political weight too low to be particularly relevant, while for many countries tribesmen will only exist in appreciable quantities in recently conquered areas where low happiness is to be expected in the first place.
In core, primary/integrated culture and state religion areas, happiness will rarely be low enough to produce any significant unrest and the primary concern of happiness is instead to maximize pop output, as these are often the most populated and productive parts of a country. Since slaves do not change their output based on happiness, the primary focus in core areas is to maximize the happiness of the highly productive nobles and then citizens, typically by building their happiness buildings in cities, importing their specific trade goods (generally only available in significant quantities a little bit into the game), and increasing civilization level (though only as a general, long term goal). Focusing on freemen happiness may also be situationally useful, but by the time a country is wealthy enough to invest in freemen it usually no longer has a pressing need for more manpower, at least as opposed to research and commerce income (from trade routes). Note that happiness is capped at 100%, which can often be exceeded by the accumulation of various bonuses by the midgame, and while it can be useful to have some buffer in case stability drops or war exhaustion increases at some point increasing happiness ceases to be useful and it can be better to invest building or trade route slots into other areas.
In contrast, recently conquered provinces of an unintegrated culture (especially of a different culture group) and different religion will be particularly difficult to please, and in general unless the country has a large number of unintegrated culture group happiness bonuses they will be virtually impossible to satisfy completely. For these areas, trying to fully manage happiness is very costly and it is easiest to just appoint a loyal, uncorrupt governor and grant him control of a large enough governor army to keep unrest and province loyalty under control in the short to medium term; if not even this is enough, the easiest way to quickly reduce the penalties from unhappiness is to try to appease any nobles and/or citizens in the province (who are normally the most unhappy as well as the largest generators of unrest), typically by building their happiness-improving buildings in the cities and/or importing the specific trade goods that improve their happiness. Over time pops will convert/assimilate and become happier, decreasing the proportion of discontent pops to the point where the garrison may no longer be needed - building theaters and temples in the main cities of the province can speed this up process significantly.
Population of each social class can change through several means: Growth/Death and Conquest.
The base rate of population growth in each city in the game is 0.04%/month. When this number reaches 100% a new pop of that type is born in that city. There are many modifiers to this value. The population growth in a city is altered by factors such as terrain type, Stability, and availability of trade goods. Note that all bonuses are additive, therefore population growth omen power may multiple the growth rate in every city you have.
- Religion: Hellenic Diety of Fertility Demeter gives a passive effect of National Population Growth: +0.1%
- Being in peace gives 0.04%/month.
- Above 50 stability gives progressively more growth rate. Having 100 stability gives 0.5%/month, while having 50 stability or lower gives 0%/month.
- Several laws give various, but very low rate of growth, typically between 0.01%/month and 0.05%/month.
- Every 12 months of stored food applies a bonus of 0.05% population growth up to a maximum of 0.5%. Provincial food storage capacity is increased by granaries and salt surplus.
- Monarchy Taxation Law: Infrastructure Policy gives National Population Growth: +0.1% and increases governor loyalty by +10 while decreasing general loyalty by -10.
If aiming to boost your population size, aim for stability (while it gives the highest potential growth rate, it is the most costly to keep high), and stored food. Having multiple of the trade goods or other modifiers have an extremely low benefit.
When a new pop starts to grow, its social class is determined by chance, from the available pops already living in the city. Its culture and religion is also determined upon it starting to grow. They are also randomly selected from the religion and culture already present in the city. For example if a city has no Tribesman then it will never start to grow. It is possible to promote all of your (for example) tribesman into freeman, and still end up with one, if it was already growing when you have promoted the already grown ones.
Population growth in a city can also become negative (by modifiers). If this happens, the growing pop will shrink instead. If there is no growing pop, an existing pop will be chosen (at random) and a progress bar toward 0 will start. If it reaches 0%, that pop will die.
Population is also gained through warfare. As cities are sacked, POWs are taken to the state capital or to the provincial capitals as slaves. It should be noted, that pops within the newly conquered city may be demoted:
- Citizen ⇒ Freemen (50% chance)
- Freemen ⇒ Slaves (50% chance)
Tribesmen and Slaves never change their social class upon conquest.
- Enslavement (From either war occupation or slave raiding. Slaves are heavily weighted to go to national or province capitals.)
- Scripted Events
- Manual movements of slaves (but not freemen or higher) by spending gold
- Tribal nations can move tribesman pops as if they are slaves.
- Tribal nations can also trigger a "tribal migration" via the Government Interface.
A slave pop can be moved from a territory to any territory in the same province or an adjacent territory.
Moving slaves costs a base of 5 gold.
- Capital surplus of vegetables lowers cost by 1 gold.
- Exporting vegetables lowers cost by 0.5 gold.
- Main article: Colonization
Pops are used to colonize unowned territories. At least 10 pops of your country's primary culture are needed in any neighboring province or up to 2 sea tiles away. Colonizing has a two year cool-down for the colonizing territory.
Each territory has a certain population capacity, which determines how large of a population a territory's terrain and infrastructure can support. Territories have a base population capacity of 10, which is modified by a number of modifiers from terrain, technology, buildings, events, and more. Knowing which territories are good for population growth is essential in city placement and economic planning; it is almost always better to construct new cities in territories with a higher base population capacity, as larger cities are almost always richer and more productive than smaller ones, and population capacity is usually the main factor that restricts the growth of cities. Note that population capacity is a different value and modifier, though related, from , which also services as a limitation to the population of a territory.
- +5 for settlements
- +20 for cities
- +30 and +10% for metropolises
- +0.25% per point of civilization value
- +10% for farmland terrain
- -10% for forest terrain
- -10% for marsh terrain
- -15% for jungle terrain
- -20% for mountains terrain
- -30% for desert terrain
- +5% if there is a nearby river
- +10% if adjacent to a major river
- +5% for coastal territories, if there is no port
- +10% if the territory has a port
- +5% for territories with a Warm Climate
- -15% for territories with a Arid Climate
- -20% for territories with a Frigid Climate
- -25% for territories with a Alpine Climate
- -75% if the province has run out of and has a Critical Food Supply
- +10 in the capital territory
- +6 in province capitals
- +20% from barracks, slave estates, mines, farming settlements, and tribal settlements
- +4 from aqueducts
- +2.5% from each State Infrastructure province investment
- +25% from the City Planning national idea
- +2% from each level of Civic Advances
- +10% from the Pedagoguery invention ( Civic Advances 8)
- +5% from the Seleukid Empire unique Imperial Calendar invention ( Oratory Advances 1)
- -20% for tribal countries
- +10% as a passive modifier of many deities (+12.5% if the holy site is held)
- +5% from Heritage of Chandragupta (Maurya)
- +10% from River Plains group heritage
It is theoretically possible to raise the population capacity of any territory as high as desired by stacking bonuses from the State Infrastructure province investment and Civic Advances, but the small percentage increases means that this is prohibitively expensive. However, as in cities and metropolises every 10 pops unlocks a new building slot, it is possible to stack city population capacity arbitrarily high (given enough time) by building aqueducts if the total of the percentage modifiers is at least 150% - possible with a reasonable number of State Infrastructure province investments by the midgame - which will make each aqueduct give +10 population capacity, enough to create another building slot to build another aqueduct once the population capacity has been filled. It is usually strongest to do this in the capital, which has a number of bonuses that makes each individual pop even more productive.
- -3 Migration Attraction
- -4% Local Population Happiness
- +1 Migration Speed
- -0.04% Local Population Growth
The population of territory with any significant amount of overpopulation will therefore usually quickly fall back down through migration and population death, while population growth from natural growth, immigration, and enslavement will be quickly stalled, providing an effective soft cap on the population that a territory can sustainably have. It is generally rarely worth having an overpopulated territory, unless the territory only needs to go slightly over the population capacity to meet the threshold to produce another trade good.
- Settlements: in monarchies and republics the base ratio is 100% slaves, in tribal nations is 50% tribesmen and 50% slaves. This can be modified building Barracks that increase the desired ratio of freemen in settlements by +75%.
- Cities: the base ratio in monarchies is 35% citizens, 35% freemen, 0% tribesmen, 30% slaves; in republics is 34% citizens, 39% freemen, 0% tribesmen, 27% slaves; in tribal nations is 33% citizens, 33% freemen, 4% tribesmen, 30% slaves.
These ratios can be modified by the local/national citizen ratio, local/national freeman ratio, local/national tribesman ratio, and local/national slave ratio modifiers, most prominently available from various laws and buildings (e.g. Libraries increase desired ratio of citizen, Mills increase ratio of slaves). The player can increase migration of non slaves pops from settlements to cities in order to promote more pops to citizen status. This is generally recommended because citizens are the only source of research and are needed to keep up in technologies.
Every social class has a promotion speed value:
- Slave promoting: +4
- Tribesman promoting: +0.4
- Freeman promoting: +4
this can be directly modified building Academies (+0.5 each), using the Social mobility edict in the province (+% based on governor finesse), enacting the second Land reform law in republics (+6).
To the values listed above are applied different modifiers. Some common modifiers include:
- Settlement: -25%
- Capital territory: 25%
- Province capital: 10%
- Coastal port: 10%
- Unrest: -1% every 0.1 unrest
- Number of Trade route: 5% every active trade route
- Road Network in territory: 2.5% for each road entering the territory
- Total population: 2.5% every pop living in the territory
- Positive centralization: 2.5% at 100 centralization
- Civic invention Granted Manumission at tech 10: 10%
- Civic invention Gradated Citizenship at tech 17: 20%