Infrastructure

Territories can be upgraded with a variety of infrastructure to improve the output and happiness of their pops, as well as its accessibility and defensibility, at the cost of gold. Investing in infrastructure can significantly improve a country's income, manpower, research, and more, and is generally most effective in more highly populated territories.

Buildings

A wide variety of different buildings can be built in territories to give a wide variety of local modifiers, such as improving pop output and happiness, adjusting the ratio of pop classes, driving assimilation and conversion, increasing the local population capacity, adding fortifications to the area, building port facilities for ships, and more. The buildings available depend on the territory's rank, with different sets available to settlements and cities/ metropolises; some of the settlement buildings are also restricted based on the trade good that the territory produces.

Every building has an associated gold cost and build time, which are modified by the build cost and build time modifiers, respectively. Each territory can only build one building at a time, though it is possible to make a queue of buildings to construct. Once it is built, buildings do not cost any maintenance or upkeep. Any building in any owned territory can be torn down instantly at any time, which returns 1/4th of the its current build cost to the treasury (also affected by the build cost modifier), regardless of when or by whom the building was built. Some events and mission results may automatically construct a building in a territory.

All

	Building	Province modifiers	Cost	Time	Notes
	Fortress	-5% Local manpower +1 Fort level +5% Local fort defense +1% Local civilization level	150	720 days	Adds 1 fort level to the territory. See Fort for other effects. Cost is additionally modified by the Fortress Building Cost modifier.
	Port	+1 Population capacity +15% Ship recruit speed +0.1 Migration attraction +0.1 Migration speed	150	180 days	Can only be built on coasts, or where ports exist at the start of the game. Adds 1 port level to the territory. See Port for other effects.

City/Metropolis only

	Building	Province modifiers	Cost	Time	Notes
	Aqueduct	+4 Population capacity	150	180 days	Requires at least 30 civilization value
	Granary	+2% Local civilization level +200 Provincial food capacity	100	180 days
	Library	+5% Local research points +2% Local civilization level +2.5% Pop conversion speed	100	180 days
	Marketplace	+2% Local civilization level +2.5% Population assimilation speed +2.5% Local base trade routes	100	180 days
	Training Camp	+10% Local manpower +2% Local civilization level	100	180 days
	Tax Office	+10% Local tax +2% Local civilization level	100	180 days
	Earthworks	-10% Population capacity +25% Local fort defense +1.00 Hostile attrition -3.00 Combat width	150	1440 days	Limit 1 per territory. Requires the Fortified Camps Martial invention Requires at least 1 fort level.
	Foundry	+25% Local Tax +25% Local Research Points +5% Local civilization level -4 slaves need for resource surplus	300	180 days	Limit 1 per territory. Requires the Blacksmith Apprentices Martial invention.
	Great Temple	+0.05 Territory provincial loyalty +10% State religion happiness +5% Local civilization level +2.00 Pop conversion speed	300	360 days	Limit 1 per territory. Requires the Open Religion Religious invention.
	Grand Theater	+0.05 Territory provincial loyalty +10% Integrated culture happiness +5% Local civilization level +2.00 Pop assimilation speed	300	360 days	Limit 1 per territory. Requires Gradual Economic Integration Oratory invention.
	Academy	+3% Local civilization level +0.01% Monthly civilization change +4% Local noble happiness +5% Local noble desired ratio	150	180 days	Limit 3 per territory.
	Court of Law	+0.01 Territory provincial loyalty +3% Local civilization level +6% Local citizen happiness +10% Local citizen desired ratio	150	180 days	Limit 3 per territory.
	Forum	+3% Local civilization level +2.5% Local monthly food modifier +6% Local freemen happiness +10% Local freemen desired ratio	150	180 days	Limit 3 per territory.
	Mill	+3% Local civilization level +6% Local slave output +6% Local slave happiness +10% Local slave desired ratio	150	180 days	Limit 3 per territory.

Settlement Only

	Building	Province modifiers	Cost	Time	Notes
	Barracks	+20% Local manpower +5% Local civilization level -25% Pop migration speed +8% Local freemen happiness +15% Local freemen desired ratio	200	180 days	Limit 1 per territory.
	Mine	+5% Local civilization level -5 Slaves needed for local surplus -25% Pop migration speed	200	730 days	Limit 1 per territory.
	Tribal Settlement	+10% Population capacity -2.5% Local citizen desired ratio +30% Local tribesmen output +8% Local tribesmen happiness	200	730 days	Limit 1 per territory.
	Slave Estate	+5% Local civilization level -25% Pop migration speed +50% Local monthly food modifier +30% Local slave output	200	730 days	Limit 1 per territory.
	Farming Settlement	+5% Local civilization level -5 Slaves needed for local surplus -25% Migration speed +50% Local monthly food modifier	200	730 days	Limit 1 per territory.
	Provincial Legation	+75% Pop migration speed +15% Pop assimilation speed	200	180 days	Limit 1 per territory.

Building slots

The number of buildings that can be built in any particular territory is limited by that territory's number of building slots. Each building takes up 1 slot, including those under construction, and no buildings can be built in a territory that has filled up all its slots. Territories that have more buildings than their number of permitted slots - for instance, after losing population during a sack - will lose any buildings over the limit. Wonders also take up a building slot, and require at least one empty building slot to begin construction.

Settlements normally only have 1 building slot (though settlement buildings are in general stronger than other buildings), which can be increased by the global settlement building slots modifier to a maximum of 2 by researching the Rural Planning Civic invention (though each settlement building will still have its territory cap of one). Building slots mostly become relevant when settlements are upgraded to cities, which gives a base of 2 extra building slots and an additional 1 for every 10 pops in the city. If a city is further upgraded to a metropolis the base number of building slots is increased to 4. Other important sources of building slots in cities and metropolises, given by the local city building slots and global city building slots modifier, include:

• +1 for the country capital
• +1 for holy sites
• +1 for all cities with a tier 3 wonder with the Engineering effect
• +2 for all cities with a tier 4 wonder with the Engineering effect
• +2 for all cities with the Urban Planning Civic invention
• +1 for all cities with the Legacy of the Builders military tradition (Levantine and Arabian traditions)
• +1 for each Make Religious Endowments religious province investment

Great wonders

Main article: Great wonders

Great wonders are special buildings that can be constructed in territories and give powerful bonuses to their local province or owner. Unlike standard buildings, wonders can be customized with various designs, materials, and effects, and are a significant investment that only the large and wealthy empires will be able to afford. As the centerpiece and defining feature of the local area, each territory can normally only support one great wonder, though certain wonders that are built by event can coexist with each other in the same territory. Uniquely, wonders usually give strong nation-wide effects that grow over time as the wonder's fame and prestige increases.

At the start of the game, there are a number of ancient wonders scattered all over the map, from the Temple of Jupiter Optimus Maximus in Rome to the Great Pyramids of Giza and the University of Taxila. Building additional wonders requires the Heirs of Alexander DLC.

Roads

Roads built by a Roman army.

Roads can be built by armies to connect two adjacent territories at the cost of gold, reducing the movement cost by 50% and effectively doubling the army movement speed between them, making them highly desirable for larger empires that would benefit from being able to move armies between their provinces more quickly. In addition to the army movement bonuses, connecting a territory to the road network also gives a minor boost to development, trade, and pop mobility, making them useful to build in highly populated developed territories as well as connecting frontier areas. Roads also appear graphically on the map as the network is built and extended, generally being most prominent on the terrain mapmode; if a road is built over a river, a bridge will appear. Unlike with buildings, roads are not associated with individual territories, but instead with pairs of adjacent territories (including possibly those connected over a strait); it is therefore possible (and common) for a territory to be a part of multiple different road segments. For every road connecting a territory to one of its adjacent territories, a territory will get the following stackable modifiers:

• +0.001% Monthly Civilization Change
• +2.5% Pop Conversion Speed
• +2.5% Pop Assimilation Speed
• +2.5% Pop Promotion Speed
• +1% Pop Demotion Speed
• +0.05 Migration Attraction
• +0.1 Pop Migration Speed
• +5% Local Base Trade Routes Modifier

There are two ways to build roads - a special, cheaper method for countries with access to Italic tradition groups, and more generic one that is available to all countries. Once a road is built, it cannot be removed or destroyed, even if the territories it connects are completely depopulated.

Regular roads

Most countries need to reach at least Level 5 of civic advances to begin building roads.

Roads can be built using the Build Road unit ability toggle, which can be activated if all of the following conditions are met:

• The unit is an army
• The army has at least 10 cohorts
• The army is not in combat, moving, or exiled
• The army is in a territory that is owned by the current country, or by one of its subjects
• The army either has no commander, or its commander is loyal (i.e. has at least 34 loyalty)

Any type of army, even levies and mercenaries, can build roads, if they meet all of the requirements.

When the build road toggle is on, road construction will begin when the unit moves from one territory to another, as long as both territories either owned and controlled by the army's owner or one of their subjects, or are uncolonized (including uninhabitable territories, though not impassable terrain). When the army arrives in that other territory, if the two territories do not already have a road between them, the road will be instantly built at a base cost of 50 gold. This cost is affected by the build roads cost modifier, given only by the Civic inventions Gromatici ( -25%) and De Architectura ( -15%). If the army has at least 1 engineer cohort, the cost of building a road is instead lowered to to 10 gold (not affected by any modifiers).

While building roads, the following modifiers are applied to the army:

• −25% Morale of Armies
• −70% Army movement without roads
• +120% Legion maintenance cost

The toggle will be turned off if the army becomes ineligible to build roads, or if the army finishes moving to a new territory without a road on the traversed connection and the country does not have enough money to build a road.

Military roads

If a country has access to Roman traditions (in the Italic traditions group), adopting the Roman Roads tradition will give access to the special Build Military Road toggle, even if it does not currently meet the technology requirements for building roads normally. Building military roads is largely the same as building regular roads, with the main differences that the road-building army can be smaller, requiring only 5 cohorts, but must be a legion, and that each road costs only 25 gold per territory connection. However, note that the cost is not affected by the build roads cost modifier. As with normal road building, the cost is lowered to to 10 gold (also not affected by any modifiers) if the army has at least 1 engineer cohort.

In addition, a reduced set of modifiers is applied to the road-building army, without the increased maintenance cost or morale penalty:

• −70% Army movement without roads

Forts

See also: Siege

Forts can be built in territories to block the advance of enemy armies and protect important cities and strategic points from being easily captured. The size of a fort is determined by its fort level, where 1 is the minimum and 0 indicates the lack of a fort, and every fortress building giving 1 fort level. This means that settlements are typically restricted to a fort level of 1, while cities and metropolises are able to support larger forts. The higher the fort level, the harder it is for an enemy army to successfully take the fort.

To fully occupy a province, the attacker must besiege its capital and any forts in the province, after which the rest will be automatically occupied after a few days. An unprotected territory takes only 15 days to occupy, while one with a fort will take multiple months to siege down unless the attacking army launches an assault (usually taking heavy casualties). Each fort level gives -1 to siege progress and provides the base garrison of 500 per fort level, adjusted by the garrison size modifier. A besieging army needs to have at least 2000 men per each fort level to begin a siege, no matter how big the garrison is. Assaulting a fort will damage the garrison, and as soon as it reaches 0, the fort will fall. When it falls (or a new fort level is built), its garrison will start replenishing at a rate of 10% of the max garrison per month.

In addition, forts exert a zone of control (ZoC) over adjacent territories. An army that enters a hostile zone of control will not be able to progress further, and must either proceed to the fort and besiege it or return to the territory they came from. Barbarians ignore all zones of control and can move freely, but territories in the zone of control of a friendly fort will not lose civilization value if occupied. Friendly forts also negate attrition from deserts or winter, and will automatically occupy any enemy-controlled territories in its zone of control unless there is a hostile army there.

Every fort level costs a base of 0.40 gold in maintenance each month, adjusted by the fort maintenance modifier, except for the first capital fort.

Every province has a certain fort infrastructure capacity value, with default capacity of 5. The first fort in a territory uses up 3 points of capacity, while subsequent fort levels only use 1, and exceeding the limit gives a +25% maintenance modifier for all forts in the province by for every point over the limit. This means, with the default limit of 5, two level 1 forts in one province would use 6 points and cost $0.4*1.25=0.5$ each per month in maintenance ( 1 in total), while a single level 2 fort costs 0.8 gold per month to maintain. Capacity can be increased through the Fortify Province province investment, several military traditions, some inventions, and a wonder effect.

Every territory in the province gets -0.25 unrest for every used fort infrastructure point, which means spreading forts out over a number of territories is much more efficient at suppressing unrest than concentrating them in a single territory, even if more expensive. As maintaining forts can be costly, it is often a good idea to remove extraneous forts that no longer serve any meaningful defensive and unrest-suppressing purpose.

Border forts

See also: Colonization

A country that has adopted the Castra military tradition from the Italic tribe traditions tree can have an army build a border fort in an owned frontier or neighbouring uncolonized territory. An army can do this action if it meets all the following conditions:

• The unit is an army
• The army has a loyal commander (defined as 34 loyalty or higher).
• The army is not in combat, moving, sieging, or exiled.
• The army has at least 5 cohorts, including at least one that is not loyal to anyone. (This requirement implictly means that mercenaries cannot be used)
• The territory the army is in:
  • Doesn't already have a fortress
  • Is uncolonized, or owned by the current country and borders a foreign (not uncolonized) territory
  • Has a free building slot
  • Borders an owned and controlled territory
  • Is not next to any other owned territory with a fortress

When the ability is activated, the country loses 3000 manpower and builds a fortress in the territory. The country then gains ownership of the province if it was previously uncolonized, in which case the territory will also gain a freeman pop of the primary culture and religion. Finally, one random cohort becomes loyal to the commander, unless the general is the ruler of a non-republic, in which case the country gains 1 tyranny instead. This ability can notably be used to colonize territories even if there is no neighbouring territory with a dominant integrated culture and state religion.

Ports

Ports are buildings that can be built in any coastal territories, as well as certain inland territories on major rivers (those that begin the game with a port). They allow ships to dock (including quickly embarking and disembarking troops), be built, repair, and supply, and are important for any nation that seeks to maintain a significant navy. The number of ports in a territory is the territory's port level, which in addition to the effects from the port buildings themselves also determines what types of ships it can build and repair: the light liburnians and triremes only require a level 1 port, the medium tetreres and hexeres require at least level 3 ports, while the very heavy octeres and mega-polyremes can only be built and repaired at ports that are at least level 5.

In addition to effects from the building itself, every coastal territory with at least one port gets the following modifiers:

• +5% Supply Limit
• +10% Pop Promotion Speed

For each territory in a province that has at least one port, the province also gets the following modifier:

• +2.5% Pop Migration Speed

Note that neither of these effects stack if territory has more than one port.

Pirate havens

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.

Destroying all ports in a pirate haven will also force any local pirate/mercenary fleets to disband, though this will not remove the pirate haven itself. If the port is ever rebuilt, the pirate fleet will eventually reappear.

Economy

Mechanics