There are hundreds of buildings and units in the game which are all connected. Each province can construct buildings and train units. Buildings are set up in a tech tree. There is no specific technology research as such, but certain advances (most notably gunpowder) do become available over time. More economic buildings such as Trading Posts, Farms or Mines, generate more money from trade, farming or mining, while military buildings allow the training of more advanced unit types. Many unit types, such as Spanish Jinetes or Polish Retainers, are called unique units and are restricted to a single faction; other units can only be trained within a single province, but can be created by any faction holding that province. Some special unit types shared by only a few factions, such as Knights Templar, are also called 'unique', though this is not strictly true. Most of the time these units appear in the form of Orders of Knighthood (Knights Templar, Teutonic Knights, Hospitallers, Knights of Santiago) and can be recruited only in conjunction with a Crusade.
Military units consist of up to 100 men (on default unit sizes), with cavalry units usually 40 strong, and certain infantry and foot archer units 60 strong, and are grouped into armies that can fight to control provinces. Fights take place on a 3D battlefield, with full tactical control given to the player (although battles can also be automatically resolved from the campaign map, speeding up games with extremely large confrontations that sometimes result in hours of battles per turn).
Faction leaders (variously called kings, emperors, sultans, khans, khalifahs, doges, grand princes or dukes) lead elite units of their own, as do their sons and brothers. The unit type for these 'royal units' is fixed for each faction: the Catholic factions all have Royal Knights, with the exception of the Swiss, who have Swiss Armoured Pikemen; Byzantine Emperors and princes fight as Kataphraktoi; princes of Novgorod or Russia lead Boyars; and Muslim factions have Ghulam Bodyguards, or Sipahi for the Ottoman Turks. Royal units without a king or prince can also be trained normally, but are expensive and (with the exception of Boyars and Kataphraktoi) under-sized compared to other cavalry units. This game also uses the YUT feature.
Ships
Ships can be built and used to control the various sea-regions. The usefulness of ships revolves around securing 'sea lanes', controlling the seas between one's own provinces and those abroad. A faction with a sea lane to a foreign port might gather intelligence on the port, land troops there, or gain income through trade. Ships can attack other ships, but all sea battles are simulated by the computer. In order to transport troops between provinces separated by an ocean a player must have control of the province from which the army will embark, have constructed a port in this province, and also control the sea lane connecting his province to the target province. As ports are normally destroyed during conquest of a province, it may be impossible to retreat after invading across the sea
Crusades
Crusades can also be 'built'. Once one has been constructed, it can be targeted at a province, have more soldiers added to it, and sent forthrightly. A crusade is the only army that can peacefully cross a foreign province (but only if the faction permits it to pass, otherwise a battle will ensue). Crusades can only be launched with the permission of the Pope (usually only against non-Catholic or excommunicated Catholic provinces), and all crusades are dependent upon the continued succession of the Papacy, such that if the Pope is conquered, the crusade will automatically disband. Each crusade is also dependent on the 'Chapter House' in the province where it was created, such that if the province where the crusade was created is conquered, or the building where the crusade 'marker' was created is destroyed, the crusade will then also automatically disband. Unless the Pope has called for a crusade against a particular faction, the launching of a crusade costs money (on top of the 3000 florin creation cost, depends on the faction's aggressions against the true Catholics) in the form of a donation to the Papacy. A crusading army is limited to the most direct course to its target, meaning that the player can only usually choose between, at most, two provinces to cross every turn; also crusades cannot be disbanded until the target has been conquered, meaning that any provinces captured during the march need to be garrisoned by the player's own troops. Each faction can only have one crusade active at a time although multiple crusade 'markers' can be built and stockpiled. Muslim nations can conversely have multiple jihads active. Jihads cost nothing extra, but can only be used to retake a province previously controlled by a Muslim faction (a sort of counter-Crusade). When first initiated, a crusade or jihad begins with a randomly generated core of soldiers (which may include otherwise unbuildable units such as religious fanatics and knights of crusading orders, such as Templars or Teutonic Knights). The controlling faction can add more soldiers to it, while others may join voluntarily as it proceeds (depending on the zeal of each province) —even defecting from another faction's armies to do so. The number of new troops joining a crusade or jihad depends on the zeal of the province that the crusade or jihad is passing through; if it is higher than 50% the army will gain strength, if it is substantially lower than 50% the army might decrease in size.
Non-military units
Non-military units, collectively referred to as 'agents', can also be trained. Christian agents include political units such as emissaries, spies and assassins, religious units such as bishops, cardinals, inquisitors, and grand inquisitors, and one royal unit, the princess (who must be born, and cannot be trained). These units for the most part conduct domestic and foreign relations. Emissaries can be used to conclude alliances (by either meeting directly with the foreign ruler, meeting with one of his emissaries, or proposing a marriage between a foreign princess and a royal male) bribe foreign armies, strip political dignitaries of previously bestowed titles, and reveal specifics about foreign provinces (such as the number of military units stationed there, and the province's technological and agricultural advances). Spies can be used to reveal much more detailed information about foreign rulers, their provinces, and their subjects, such as specific strengths and weaknesses that could be utilized to a ruler's advantage. Assassins can be ordered to kill both foreign and domestic units, be they rulers, generals, princes, or other agents. Assassinating foreign rulers temporarily decreases the loyalty of that ruler's provinces, and the valour and morale of enemy military units. If the ruler has no heirs the faction is eliminated from contention (except for the Holy Roman Empire, which elects a new emperor if there are no heirs able to control the throne, and the Papacy, whose popes do not produce heirs and are always elected). Assassinating a general decreases the valour and morale of the units that were under that general's command. Assassinating a religious unit can halt the spread of that faction's faith. Assassinating political agents puts a stop to whatever service they were performing, such as seeking an alliance or spying. Ordering the assassination of one's own units can eliminate militaristic or religious trouble makers (such as cowardly generals or over-zealous inquisitors), or future heirs (whose negative or incompetent attributes may cause riots or disloyalty were they to ascend the throne). The more important and significant the assassin's target is, the less likely he is to succeed; in some cases, such as a well guarded emperor or khalifah, the assassin's likelihood of success can be listed as 0%. Bishops and cardinals increase the zeal of a province and spread the faith of their ruler. Inquisitors and grand inquisitors greatly increase the zeal of a province, and can root out heresy and religious malcontent in a province. Through marriage, princesses can forge alliances with foreign rulers or strengthen ties of loyalty between a ruler and his generals.
Agents and military commanders have various attributes indicating their skill. For agents, this is simply a rating, from zero upwards, referred to as 'rank' or 'valour'. The higher their rating, the more effective they are in their services (emissaries are more successful at bribing armies, resisting assassination, or forming alliances; assassins are more likely to kill their assigned targets; religious units resist assassination and spread their relative faith faster). Generals also have rank as their Command ability, but are also rated on Loyalty (or Influence for a faction leader), Piety, Dread and Acumen. These influence their ability to govern a province as well as command battles. A pious governor will improve the loyalty of a zealous population of the same religion, while one with great acumen will increase the income from his province. Sometimes, a unit will be trained with unusually high abilities and the name of a famous historical figure. For example, Saxo Grammaticus or Thomas à Becket appear as three-rank bishops, while commanders like Tancred de Normandie, Joan of Arc, Frederick Barbarossa, Richard the Lionheart, Saladin, Alexius I Comnenus, Robin of Locksley, Henry the Lion, Llywelyn the Great or El Cid are great generals and leaders.
On top of these ratings, it is possible to shape the personality of individual kings and generals. The progression of time, and notable actions performed by generals, often lead to them gaining certain 'traits', called Vices and Virtues, that can influence their ratings and certain other values. For example, a general who often retreats is seen as a coward, and his men will be more likely to run away themselves in the future. A general who orders the execution of captured rebels generates a reputation for bloodthirstiness and increases Dread (a good thing), but also robs his soldiers of their share of ransom money and thereby decreases their morale (a bad thing). Moving the "princess" icon onto a relative will give them the "incest" attribute, which, if revealed by a spy, will cause a significant loss in that character's Piety rating, and can cause rioting and uprising in particularly zealous provinces. Many Vices and Virtues will, however, be acquired randomly
Rebellions and Civil Wars
Rebellions occur if the loyalty of a particular province falls too low and it works in much the same way as in Shogun Total War. Province loyalty can be influenced by a number of factors such as the tax level number of troops and number of turns it would take the ruler to reach the province. If for any reason it becomes impossible for the ruler to reach a province then the loyalty will plummet. Getting your ruler trapped on an island, say, can lead to a massive general revolt. Civil Wars do not differ greatly from rebellions in effect - only in cause. If a large number of unit commanders have low loyalty then there is potentially a civil war. This will be triggered if there is a large stack commanded by a disloyal general who will lead the rebellion. During a civil war, generals with higher loyalty will remain under control of the current ruler, while those with low loyalty (usually three or lower) will join the rebellion. The player is given the choice to back the rebels and there may be something to gain by engineering a civil war if you can so replace a poor ruler. Leaders with high enough Piety can command support from the religious population of a province if that province is conquered by another faction of differing religion (an army will appear under player control).
It had been planned to allow other kingdoms who had established a prior claim to the throne by marriage to princesses to join in a civil war to claim the throne for themselves. However this was never implemented.