From Imperator Wiki
Revision as of 06:25, 27 July 2019 by Wethospu (talk | contribs) (Created page with "Assaults are an alternative way to capture forts. In an assault, unmounted units attempt to overpower fort's garrison in land combat. Compared to sieging, an assault can capt...")
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to navigation Jump to search

Assaults are an alternative way to capture forts. In an assault, unmounted units attempt to overpower fort's garrison in land combat.

Compared to sieging, an assault can capture a fort much faster but results in more casualties. A common use for an assault is to either retake a recently captured fort or finish up a siege when the fort has been breached. An assault can also be used to capture unharmed forts by micromanaging the assault.

Assaults have hidden mechanics which severely punish sending too few or too many units which often leads to massive casualties.

Key elements for an assault

  • Fort level: Higher fort levels require more units for the assault. This also leads to more casualties.
  • Dice: Random dice rolls determine base damage for both sides.
  • Army: Non-mounted units in the army participate in the assault.
  • General: Martial level of the general increases strength of the assault which reduces casualties.

When to assault

Exact conditions for assaulting are difficult to calculate because of random dice rolls and multiple variables affecting each other.

Some recommendations can be gived based on calculating results on different situations.

  • Forts should be assaulted when they have less than 50% garrison remaining.
  • With a breach, the fort should have less than 75% garrison remaining.
  • There is still a small chance (< 10%) that the assault runs out of morale before the fort is captured.
  • However the weakened garrison should surrender on the next siege tick.
  • Recommended amount is ~4 units per fort level.
  • General with 5+ martial needs ~3 units per fort level.
  • General with 10+ martial needs ~2 units per fort level.
  • These value give a good chance to capture the fort with reasonable casualties.
  • Add 50% more units if you want to prepare for the worst case. However this will increase casualties in most cases.
  • You can remove 33% of the units if the fort has less than 25% garrison remaining (or less than 50% with a breach).
  • Consolidating can be used during the assault to reduce casualties but it doesn't really affect the recommended amount of units.

Please report results of following these recommendations in the discussion page, especially on failures.


Forts can be assaulted optimally by micromanaging the assault. This works even for unharmed forts.

  1. Check how many units (table below, second number) are needed to win the assault in the worst case scenario.
  2. Send all units (Light Infantry) and enough mounted units (Light Cavalry) to the fort.
  3. Check how many units are needed for optimal assault (table below, first number). Create a new unit from rest of the units.
  4. Move this new unit to any adjacent tile. These units get removed from the assault force.
  5. Start the assault and unpause.
  6. When the manpower drops below optimal, move units back to the fort.
  7. Also move units back if 7 days have passed (to prevent their movement getting locked).
  8. Merge and consolidate units. Again split excess units and move them to any adjacent tile.
  9. Remember to keep one unit with a high morale in the assault. Other units can fight without any morale.
  10. Repeat until the assault is over.
Martial skill 0+ 5+ 10+ 15+ 20+
Fort level 1 3 of 9 2 of 6 2 of 6 1 of 4 1 of 3
Fort level 2 6 of 17 4 of 11 3 of 9 2 of 7 2 of 6
Fort level 3 9 of 25 6 of 20 4 of 13 4 of 11 3 of 9

Maximum losses can also be calculated from the table above (second number - first number). With balanced dice rolls, losses and required units are reduced by ~50%. With optimal dice rolls, losses and required units are reduced by ~66%. So most likely optimal execution is not needed.


Dice & Damage

  • An assault has a base damage of 0.1.
  • A fort has a base damage of 0.2 and a 90% damage reduction.
  • Each side rolls a dice from 1 to 6 every 5 days, increasing the base damage 0.02 per pip.
  • A breach reduces the base damage by 0.1 which means the assault takes 33% - 50% less damage.
  • A full strength assault deals damage equal 3% - 6% of maximum garrison.
  • A full strength garrison deals damage equal 6.66% - 10% of maximum assault (3.33% - 6.67% with a breach).
  • The garrison deals damage all units in the assault.


  • Only Archers, Heavy Infantry and Light Infantry can participate in assaults.
  • All unit types are equally effective at assaulting. But Light Infantry should be preferred because of their lower attrition weight.
  • All modifiers such as discipline, offense, defense, morale damage taken, etc. don't have any effect at assaulting.
  • An assault requires an active siece which needs at least 5000 manpower per fort level. Any units count for this limit.
  • The assault stops instantly if the manpower drops below the limit.
  • The army should have extra units to cover losses from the assault and also from attrition.
  • Assaulting units can also be moved away from the fort to stop the assault. This may also stop the siege unless you have enough units.
  • All valid units participate in the assault, even if they are in a different army.
  • The army should have units that can't participate in assaults (like Light Cavalry) to keep the siege active.
  • It's recomennded to assault with only a single unit type because consolidating during the assault reduces casualties.

Fort level

  • Every fort level adds 1000 manpower to the maximum garrison size. Garrison size can be modified with Fort Maintenance setting.
  • Every fort level increases combat width by 3000.
  • Combat width sets the minimum amount of manpower required to assault effectively.
  • Combat width also sets the maximum amount of manpower which can deal damage to the garrison.


  • Martial skill of the general increases the assault ability by 10% per level (the tooltip states 5% per level which is incorrect).
  • Assault ability can also be increased from an invention.
  • Assault ability increases strength of the assault which means that less units are needed to assault effectively.

Optimal amount of manpower

Fort level and assault ability (mainly from general's martial skill) determines the optimal amount of manpower. Values are calculated below:

Martial skill 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Fort level 1 3000 2728 2500 2308 2143 2000 1875 1765 1667 1579 1500 1429 1364 1305 1250 1200 1154 1112 1072 1035 1000
Fort level 2 6000 5455 5000 4616 4286 4000 3750 3530 3334 3158 3000 2858 2728 2609 2500 2400 2308 2223 2143 2069 2000
Fort level 3 9000 8182 7500 6924 6429 6000 5625 5295 5000 4737 4500 4286 4092 3914 3750 3600 3462 3334 3215 3104 3000

If the assault doesn't have enough manpower:

  • Assault deals reduced damage (proportional to how much manpower is missing).
  • Assault takes increased damage (proportional to how much manpower is missing).
  • For example with 50% manpower the assault takes double damage. This will quickly destroy any remaining forces.

If the assault has too much manpower:

  • Damage doesn't increase over the limit so damage from extra units is wasted.
  • All units still take damage which results in bigger losses.

Damage formula

Common variables:

 combat_width = 3 * fort_level
 assault_ability = 0.1 * martial_skill + other_sources
 effective_assault_strength = min(assault_strength * (1 + assault_ability), combat_width) 

Fort damage

Fort deals damage to all units in the assault.

 base_damage = 0.2 + 0.02 * roll - 0.1 (with breach) 
 morale_damage = base_damage
 strength_damage = base_damage * fort_strength / effective_assault_strength

Assault damage

 base_damage = 0.1 + 0.02 * roll
 strength damage = base_damage * 0.1 *  effective_assault_strength