Combat in Imperator occurs when two armies are in the same city. The army first in the city is considered the defender, unless the other side has control over fortifications in the province.
In Imperator, there is a Primary Frontline and a Secondary Frontline. The First Frontline will enter battle first, damaging the opposing side until its morale breaks or it suffers enough damage to be eliminated. The Secondary Frontline will then begin to move forward to become the new front. On the sides the units designated as Flank units will be deployed, these will first fight and kill the opposing flank, and then start targeting the center if they can.
In the army interface, you will be able to select which unit type you want to be prioritized for First Frontline, Second Frontline and Flank. The preselected choices will depend on your Military Traditions but they can be changed freely by the player or the AI for each army. The size of the flank can also be set, either 2 cohorts, 5 cohorts or 10 cohorts.
Additionally some unit types are now scripted to be able to deal or take more morale damage or more physical damage, making them more or less suited for each role. In most cases this means that you might see a first skirmish phase where your Primary Frontline of Archers or Light Infantry try to do as much damage as possible to the other side before their morale breaks and they retreat. They are then followed by the units of the Second Frontline, potentially composed of heavier units such as Heavy Infantry or/and Elephants.
In an ideal world you might choose to deploy something like Horse Archers on the Flanks, with a high maneuver value that would allow them to deal damage far into the center once they have defeated the opposing flank, but you might also go for something specifically to prioritize countering the opposing flank.
When you do not have enough of your preferred unit type for a role the game will fill out with units in order of how high their build cost are.
Each day, each unit will fire on one target in front of them, or towards the side, if they have a high enough flanking ability. Damage is determined by adding up the dice with the combat modifiers from terrain and leaders, where a total of 0 or below gives 2% damage, and the maximum of 15 from terrain and dice gives 30% of damage.
Crossing a river, or doing a naval landing, gives -1 to the attacker. Mountains gives +2 to the defender, while Hills, March and Forests gives +1 to the defender. Leaders impact combat as well, with the difference in martial giving a bonus to the one with the highest martial. Then the damage value is modified by the following before being applied to the target. If you are firing from the back line, you are basically at 50% efficiency.
One of the more major difference-makers in combat is the tactics. For each army you can determine one offensive and defensive tactic, which each has 1 they are great versus, and 1 they are bad versus.
The offensive tactic is used if you are the **attacker** in a battle, and the defensive tactic is used if you are *not* the attacker.
All Out Assault +30% versus Withdraw +20% versus Probing Counter Attack -20% versus Hard Defence Both sides takes +10% casualties.
Frontal Assault +20% versus Withdraw +10% versus Probing Counter Attack -10% versus Hard Defence
Outflanking Attack +10% versus Strong Counter Attack -10% versus Mobile Defence
Echelon Attack +10% versus Mobile Defence -10% versus Probing Counter Attack
Probing Attack -10% versus Strong Counter Attack +10% versus Hard Defence Both sides takes 25% less casualties
Strong Counter Attack +10% versus Probing Attack -10% versus Outflanking Attack
Probing Counter Attack +10% versus Echelon Attack -10% All Out Assault -10% Frontal Assault
Hard Defence +10% All Out Assault +10% Frontal Assault -10% Probing Attack
Mobile Defence +10% Outflanking Attack -10% Echelon Attack
Withdraw Both sides takes 25% less casualties.