Land combat in Imperator occurs when at least two armies of states currently at war with each other are in the same territory. The army that entered the territory first is considered the defender, unless the other side has control over fortifications in the province.
On each side, more than 1 army can partake in combat. The simplest way to achieve this is by attaching armies to a leading army. Armies may be attached to allied armies or to the state's own.
Battle chess board
In Imperator: Rome, the battle chess board is divided into squares, grouped into 2 rows with 30 squares each. Each side has a single row. One cohort fills one square.
- Main article: Deployment
At the start of a battle, cohorts from both armies deploy on the battlefield. Deployment may also happen during the battle when cohorts retreat or new armies join the battle (often referred as reinforcement).
The order of deployment can be customized by selecting preferred unit types.
Morale represents the willingness of an army's soldiers to fight. Every cohort in an army has an individual morale value, which can range from 0 to a base maximum of 3 (adjusted by the Morale of Armies modifier), which is then averaged over all the cohorts to give the army's overall morale. Levies are raised at full morale, but legions and mercenaries start at 0 morale when raised and will take some time before they are ready for battle. If a cohort has less than its maximum possible morale, it will gain a certain percentage of its maximum morale each month based on its Army Morale Recovery modifier. The army morale recovery modifier is highly dependent on the ruler's martial skill which can be problematic for countries with a low martial, but can be increased at the cost of higher maintenance with the Unit Reorganization unit ability.
When in battle, cohorts inflict damage to both morale and strength. Cohorts that lose all of their morale withdraw from the battle and will no longer fight, and if all of an army's cohorts have lost their morale it will be forced to concede the battle and retreat. Most battles are decided by which army loses all its morale and retreats first; it is rare for an army or cohort to fight all the way to the point of annihilation unless it is already weak or is completely overwhelmed. This can allow an army to emerge victorious over another army that is larger or nominally stronger if it has higher morale or is otherwise more effective at inflicting morale damage, and can be particularly decisive in the early game.
- Main article: Damage formula
Each day, each cohort in the first battle row of each side will attack another within its range. A unit type's range in squares is equal to its maneuver value.
The opposing cohorts inflict strength-damage and morale-damage.
Casualties and morale depletion are applied at the end of each day to each cohort taking part in the battle. The Attacker-role and Defender-role are calculated the the same way, but may be subject to some modifiers.
Each cohort has separate base values for strength-damage and morale-damage. These are subject to a random dice roll every 5 days and by other modifiers.
At the end of each day units with less than 0.25 Morale disengage until the end of the battle. On the next day, other units or reserves fill in the ranks to take their place. The day after the last available unit from either side disengages, combat ends and the defeated army is forced into a shattered retreat.
Unlike some other games (e.g. CK2), there is no pursuit phase where the victors run down and inflict heavy casualties upon the broken forces.
After 5 days of combat have passed, it becomes possible to order a retreat by ordering an army to move to another territory. At that point the battle is considered lost with corresponding reduction of the warscore and losses to the general's popularity.
Each army in a combat engagement can be separately ordered to retreat by selecting it from the outliner. Any remaining armies continue fighting and deploying reserves to fill in abandoned positions.
Stack wiping means that one side of a battle gets totally wiped out, losing all of its men. This usually happens when one side is much stronger than the other. The exact rules are:
- Total manpower is greater than 10x of the enemy manpower. This is checked at start and also at end of the battle.
- Enemy can't deploy any cohorts. This happens when all cohorts have less than 0.25 morale.
- Enemy is defeated before retreat is possible and total manpower is greater than 2x of the enemy manpower.
If both sides would stack wipe then only the defender stack wipes.
Tips: Largest impact
In summary, the variables that impact the combat the most are:
- For morale damage - current morale. A unit at full morale does 5x morale damage of a unit that is on low maintenance.
- With small armies - flanking/maneuver. Flanking with 5 horse archers on each side makes enemy side units take 6x damage, while horse archers themselves stay at full morale and manpower.
- General skill and terrain. A 5 pip advantage (e.g. 10 skill general vs 1 skill general) gives +100% base damage.
- Heavily countering unit types. E.g. Light Cavalry vs Heavy Infantry does only 50% normal damage.
- Low manpower. A battered non-consolidated 500-man cohort will only do 50% of the damage of a full 1000-man cohort, while still taking a full space on the front line.
(see concept: modifiers)
The martial skill of the commanders of each army are compared, with a +1 bonus given to the army of the better general for every 2 levels of difference in skill.
- Main article: Terrain types
The attacker receives one or more penalties depending on the territory's terrain and map features.
The defender never suffers terrain penalties.
The value can only be zero or less, it cannot be positive.
- Hills, Marsh and Forests give -1 to the attacker
- Mountains give -2 to the attacker
The following penalties stack on top of any terrain effect:
- Crossing a river -1
- Attempting a naval landing -2
- Crossing a strait -2
Thus the maximum possible penalty is -4 (E.G. a naval landing into mountains).
Discipline is a generalized summary of various modifiers to damage done in battle. It exists as an overview to aid players. Discipline doesn't reduce damage taken unlike what the tooltip may mention. Discipline itself is a value that serves solely as a modifier, and then other modifiers may adjust the discipline value further. It is calculated on a state level per unit type. When pressing the military button in the top bar, it is possible to see the current modifiers for all unit types.
A unit's final discipline value is determined by a combination of factors including:
The martial skill of the character holding the state's "Military tribune" position, some Inventions, some trade goods, the Blessing of Mars, and many other factors.
Most sources of discipline stack additively which means two sources of +10% discipline ends up as +20% discipline. The exception to this rule is cohort's personal loyalty which increases total discipline by 10%.
- "Experience" redirects here. For the related nationwide value used to purchase military traditions, see Military experience.
Every cohort has an experience value out of 100% that represents how well trained the cohort is. Every point of experience gives -0.3% damage reduction, for a maximum of -30% damage taken in combat at 100% experience. Archers have a slightly increased damage reduction because of extra morale damage taken. Similarly Heavy Infantry, Light Infantry and War Elephants have a slightly decreased damage reduction.
The Cohort Starting Experience and Starting Experience modifiers increase the experience that newly raised levies and newly recruited legion cohorts start with (with the starting experience modifier also increasing the experience of newly built ships), and when focused on can add up to a substantial amount of experience.
After a cohort is raised, one of the main way it accumulates experience is through fighting battles. After each battle, every cohort involved will gain experience based on the number of casualties their side took, giving the following formula:
Cohorts can also passively gain experience through the Monthly Experience Gain modifier, which gives a flat modifier to the change in experience per month. The most common way to increase cohort experience this way is to use the Drill Army action for legions, which gives a +2.50% monthly experience gain bonus (at the cost of increased army maintenance and cohort loyalty gain chance).
Every month, cohort experience also decays according to the cohort's total Experience Decay modifier, with a base of +4.50% experience decay per month. This decay can be reduced by various ideas, deities, inventions, and military traditions, but is capped at 0% (it is not possible for cohorts to gain experience through negative decay). Note that unlike the monthly experience gain modifier, which is a flat increase or decrease in experience points per month, experience decay reduces cohort experience by a certain percentage of its current experience per month. For instance, a cohort with 30% experience will have a base experience decay of 4.50% × 30 = 1.35, and assuming no other changes will have its experience reduced to 28.65% at the beginning of the next month. This means that generally, cohort experience will decay much faster at higher values than lower values. There is no extra experience decay when cohorts are reinforcing.
Cohort experience is converted into military experience in two different ways. The average cohort experience across all armies increases the country's passive monthly military experience gain by +0.006 per point (up to a maximum of +0.60 military experience if all cohorts have 100% experience), which is mostly relevant for legions (especially during peacetime). As well, levies that have been raised for at least 8 months will grant 0.015 military experience per point of cohort experience for each disbanded cohort.
- "Combat tactics" redirects here. For naval combat tactics, see Naval warfare § Combat tactics.
Every army can be assigned a particular combat tactic that they will attempt to use in battle against other armies. The available combat tactics add a rock-paper-scissors-Spock-lizard-mechanic to battles - each tactic is strong against two other tactics, and poor against two others. Combat tactics have the following properties:
- The modifier applies to the damage done.
- The positive modifier applies only to certain unit types, and can be different for each type. The displayed "total effectiveness" of a tactic is the average of the tactic's effectiveness over each of the army's cohorts.
- The negative modifier applies fully regardless of army's composition.
- The casualties modifier applies to both armies.
- Every army always has a combat tactic chosen from the available list, with the default being Shock Action.
- The combat tactic can be changed at any time prior to a battle at no cost or cooldown.
- An army's combat tactic cannot be changed once a battle has been started, but can be overridden if a larger allied army subsequently joins the battle.
The effect of any specific tactic is not overwhelmingly powerful. See Tips: Largest impact above to compare the magnitude of other combat modifiers.
These five tactics are available to all countries at all times.
|Tactic||Unit effectiveness||Against other tactics||Casualties||Description|
|Bottleneck||Against a massed charge, nothing performs better than a solid defensive line. However, if the enemy is clever enough to pick us off one by one, we may encounter problems.
|Deception||A staggered assault can wear down an enemy's resolve faster than one might imagine, and allows us to respond to mobile threats with great ease. The greatest weakness of this tactic stems from our vulnerability to skirmishing behavior.
|Envelopment||Drawing forth an enemy counterattack, and then plunging into the side of their exposed formation can cause massive losses. Against an enemy who can quickly martial their men to multiple fronts however, increases the risk of this maneuver.
|Shock Action||+10%||Sometimes, caution must be thrown to the wind - few foes can stand against a massed charge, though we must be wary of those that can field a staunch defense.
This is the default tactic for any new army
|Skirmishing||−25%||If the enemy exposes a series of flanks for us to harry, this maneuver will surely pay off. We should not employ this tactic against stalwart offensive lines, however.|
These other tactics are only unlocked by adopting specific military traditions.
|Tactic||Unit effectiveness||Against other tactics||Casualties||Description|
|Cavalry Skirmish||−10%||Ordering cavalry to harass and skirmish, rather than remain in formation, can often be used as a tool to deny an entire flank to hostile troops.
|Hit-and-Run||−10%||In the face of an overwhelming enemy an asymmetric approach can often be more successful than a head-on one. Ambushes, raids, and hit-and-run style tactics were common in ancient warfare, especially in Gaul, Germania, and Iberia
Requires the Barbarian military tradition "Ambush".
|Padma Vyuha||−10%||A highly complex defensive formation, the labyrinthine appearance of the Padma Vyuha is designed to confuse and misdirect foes while defending more vulnerable friendly troops at the core.
Requires the Indian military tradition "Padma Vyuha".
|Phalanx||−10%||The Phalanx originated as a highly defensive method of formation fighting, used primarily by Greek city-states. It was further developed by the Macedonian military, who built their armies around a heavily armored Phalanx formation.
|Triplex Acies||Like the Hellenistic Phalanx the Roman tactic formation known as the Triplex Acies, or triple lines, is inspired by the Phalanx of the Greek City states. Where the Macedonian or Hellenistic Phalanx has gone for cohesion the Roman Formation instead emphasized flexibility.
Requires the Italic military tradition "Triplex Acies".
Besides the damage inflicted on each army, battles also have direct political and personal consequences for army's commanders and the war as a whole.
- Main article: Warscore
The side that wins the battle - either by forcing the other side to retreat first, or completely destroying all the enemy armies involved in the battle - gains warscore depending on how many casualties each side took in the battle as a proportion of the number of soldiers involved. The exact formula can be calculated as:
Counterintuitively, this formula means that the winning side gets more warscore if they take more casualties (as well as from inflicting more casualties on the enemy side). In particular, it means that a stackwipe with zero losses on one side will give that side +3 warscore, while a battle where both sides are nearly wiped out will give up to +6 warscore.
The maximum possible warscore from all battles (including both land and naval battles) is 25. Superiority wargoals will also give additional ticking warscore to the side that has a net total of at least +10 warscore from battles.
- Main article: War exhaustion
Once a battle concludes, each side takes war exhaustion based on their number of casualties as a proportion of their total maximum army strength. The total maximum army strength is calculated as how large the country's army would be (not including mercenaries or other special armies) if all of its legions and levies were at full strength, which is equivalent to the following formula:
Note that the total levy strength is equal to how many levy cohorts the country would have if they were all raised at that moment. This is not necessarily the same as the number of levy cohorts that the country actually has currently raised, since population growth or decline in the region means that the strength of the levy may have changed since the levy was raised. Overall, this means that less populous countries and those with a smaller total army strength take more war exhaustion from the same amount of casualties than more populous country would.
- Main article: Popularity
An army's commander is considered personally responsible for the outcome of any battles, and will gain or lose popularity depending on the outcome of battles they are involved in. After any battle ends, the commander of the winning side will gain popularity and the commander of the losing side will lose popularity based on the casualties that they have inflicted on the other side, according to the following formula:
Note that for the losing side, the result of the formula is multiplied by -1 (i.e. made negative) in order to get the amount of popularity that the losing commander loses. As well, note that while the winning side gains popularity depending on how many casualties they inflicted on the losing side, the losing commander loses popularity depending on how many casualties the winning side (not the losing side) took. As with warscore, this somewhat counterintuitively means that a defeated commander will lose more popularity if their side inflicts more casualties, as long as they still end up losing the battle in the end.