基础设施

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, 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 build cost to the treasury (regardless of when or by whom the building was built).

Military

	Building	Province modifiers	Cost	Time	Territory rank
	Training Camp	+10% Local manpower	50	180 days	City
	Fortress	+1 Fort level	100	915 days	City/Settlement
	Foundry	+5% Starting experience +1% Population output	50	180 days	City

Economic/Management

	Building	Province modifiers	Cost	Time	Territory rank
	Market	+2.5% Local base trade routes	50	180 days	City
	Tax Office	+10% Local tax	50	180 days	City
	Academy	+7.50% Local research points +1% Local noble desired ratio	50	180 days	City

Population

	Building	Province modifiers	Cost	Time	Territory rank	Requirements
	Granary	+200 Provincial food capacity	50	180 days	City
	Library	+4% Local noble happiness +2% Local noble desired ratio	50	180 days	City
	Court of Law	+3% Local citizen happiness +6% Local citizen desired ratio	50	180 days	City
	Forum	+3% Local freemen happiness +6% Local freemen desired ratio	50	180 days	City
	Mill	+3% Local slave output +4% Local slave happiness +6% Local slave desired ratio	50	180 days	City
	Temple	+3% State religion happiness +1.00 Pop conversion speed	50	180 days	City
	Theater	+3% Integrated culture happiness +1.00 Pop assimilation speed	50	180 days	City
	Aqueduct	+4 Population capacity	50	180 days	City	Has at least 30 civilization value

Settlement Only

	Building	Province modifiers	Cost	Time	Territory rank	Requirements
	Barracks	+20% Population capacity +20% Local manpower +8% Local freemen happiness +15% Local freemen desired ratio	120	180 days	Settlement	None
	Slave Estate	+20% Population capacity +50% Local monthly food modifier +30% Local slave output	120	730 days	Settlement	None
	Mine	+20% Population capacity -5 Slaves needed for local surplus	120	730 days	Settlement	Produces , , , , or
	Farming Settlement	+20% Population capacity -5 Slaves needed for local surplus +50% Local monthly food modifier	120	730 days	Settlement	Produces , , or
	Tribal Settlement	+20% Population capacity +30% Local tribesmen output +8% Local tribesmen happiness	120	730 days	Settlement	None
	Provincial Legation	+75% Pop migration speed +0.20 Pop assimilation speed	120	180 days	Settlement	None

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, any buildings over the limit will be lost.

Settlements always have 1 building slot and this cannot be increased, so they can only ever have a single building. When settlements are upgraded to cities, they get a base of 2 extra building slots and an additional 1 for every 10 pops in the city. If the city is further upgraded to a metropolis the base number of building slots is increased to 4. Other important sources of building slots include:

• +1 for the country capital
• +1 for holy sites
• +1 for all cities with the Urban Planning invention ( Civic Advances 18)
• +1 for all cities with the Legacy of the Builders military tradition (Levantine and Arabian traditions)

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
• +0.05 Pop Migration Speed
• +0.05% Local Base Trade Routes Modifier

There are two ways to build roads - one for countries with Italic traditions, and one for countries with any other military tradition set. 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)

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. When the army arrives in that other territory, if those 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, given only as a -25% modifier from the Gromatici invention ( Civic Advances 15).

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

• −25% Morale of Armies
• −70% Army movement without roads
• +120% Army 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.

Roman roads

Countries with Italic military traditions need to pick the Roman Roads tradition from the Roman path to unlock road construction, even if they have already meet the requirements for normal road construction. Otherwise, building Roman 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, and that each road costs only 25 gold per territory connection. However, note that this cost is not affected by the build roads cost modifier.

As well, 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

参见：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, with 1 as the minimum and 0 indicating the lack of a fort in the territory; all country capitals start with 1 fort level by default, and every fortress building adds 1 further fort level. Note that this means that settlements are generally restricted to a fort level of 1, with only cities and metropolises able to support larger forts. Each fort level gives -1 to siege progress and provide the base garrison of 1000 per fort level, adjusted by the garrison size modifier. An besieging army needs to be at least 4 times as large as the garrison to begin a siege, and when a fortress falls (or a new fort level is built), its garrison will need to be replenished at a rate of 10% of the max garrison per month. Forts with a high fort level will therefore need both a large commitment of forces and a significant amount of waiting to successfully take, and can be a potent defensive measure at important chokepoints.

In addition to the opportunity cost of taking up a building slot, every fort also costs a base of 0.50 gold in maintenance each month, adjusted by the fort maintenance modifier. Fortifications are therefore quite costly, particularly for smaller countries, and it is often a good idea to remove extraneous forts that no longer serve any menaningful defensive purpose if the maintenance costs are becoming an issue.

One of the main effects of a fort is that it prevents enemy armies from being able to occupy the territory after the base occupation time of 15 days, but instead requires the attacker to successfully siege or assault the fort before the territory can be occupied. In addition, forts exert an zone of control over the adjacent territories, restricting enemy movement and controlling nearby territories. An army that enters a hostile zone of control will not be able to progress further, and must instead either proceed to the fort and besiege it or return to the territory they came from - in this way, a line of forts one or two territories apart can completely block an enemy army from progressing past it, and can be useful along contested frontiers or to protect valuable core areas. As well, any hostile territory within a zone of control of a fort that is not being besieged will have occupation progress as though an army was occupying it, unless an army on the same side as the current controller is currently in the territory; if a territory lies in the zones of control of multiple hostile forts, it will continually switch occupation every several days between each side. Territories within a friendly zone of control will also not lose civilization value when occupied by barbarians, making them useful to build near barbarian strongholds. Zone of controls are fully active for not only owned and controlled forts within the country, but also controlled forts within enemy nations, making it possible for a counteroffensive into previously occupied territory to be blocked by a country's own occupied forts.

Border forts

参见：Colonization

A country with the Italic military tradition Castra (from the Roman path) 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.
• 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.

经济

机制