Information compiled from the actual source code and published courtesy of Paradox. Enjoy!
What are the siege parameters?
In the Siege information window:
- The number on the left is that attacker siege value
- The number on the right is the defender siege value.
How is the attacker siege value computed:
The attacker siege value is the addition of:
- The best siege capabilities among the attackers leaders
- An artillery bonus that depends on the number of artillery and the fortress level:
Fortress level ranges from 1 (minimal) to 6 (maximum).
If the number of artillery is greater than or equals to 40 * fortress level, artillery bonus is +3.
else if the number of artillery is greater than or equals to 25 * fortress level, artillery bonus is +2.
else if the number of artillery is greater than or equals to 10 * fortress level, artillery bonus is +1.
else the artillery bonus is 0.
How is the defender siege value computed:
The defender siege value is the addition of:
- The siege ranking of the fortress unit (I guess this is the default siege capabilities of the country's default leaders)
- The fortress level, from 1 to 6,
- The terrain modifier, which is 0 for plains and 2 for all other terrains,
Two other parameters are substracted to the defender siege value (causing it to become negative):
- A progress variable named P, ranging from 0 to 8 and representing successful offensive actions against the defenders
- A duration variable D, that grows over time (+0.3 per siege cycle, see below) if the city is not a not blockaded coastal province.
How does the siege evolves?
At the end of each siege cycle (usually once per month, although siege are faster during the Napoleonic land era), the siege evolves.
First, if the defender forces are reduced to less than 100 men, there is a great chance that they surrender.
Then, a randomly generated number, modified by both sides' siege values represents the siege progress:
What is extra attrition? Each time the extra addition is increased, an amount of the side troops die. For instance, if the defender extra attrition was 7%, and is increased by 1%, then 8% of the defender troops die. It is applied immediately and not at the beginning of the month.
Important note: Extra attrition will only be applied correctly in the next 1.06 patch.
Finally, the D parameter is updated. It represents the defender weariness, its lack of supply.
If the province has a not blockaded port, then D is decreased by 0.3 up to 0.
If the province has no port, or if its port is blockaded, then D is increased by 0.3.
What are the effect of breaches:
If there has been at least one breach, the fortress level is not substracted from the attackers shock & fire values during assault.
Case study #1: Siege a plain province with a level 1 fortress but no port, with a +1 siege leader on your side
Attacker siege value = 1 (+1 leader, no cannons)
Defender siege value = 1 (fortress) + 0 (terrain) - P - D.
D will increase by 0.3 each month.
P will increase over time to its maximum value of 8.
Initial modifier (P=0, D=0) = 0, modified result ranging from 1 to 10:
After 8 month, D = 3.2 (3), modifier is +3, modified result ranges from 4 to 14 even if P is still at 0 so you are able to win the siege (10% chance each turn).
Case study #2: Siege a forest province with a level 3 fortress and a not blockaded port, with no good siege leader on your side
Attacker siege value = 0 (no leader, no cannons)
Defender siege value = 3 (fortress) + 2 (terrain) - P - D.
As the province port is not blockaded, D will not increase and stays at 0.
P will increase over time to its maximum value of 8.
So the minimal defender siege value is -3. Whatever the random number is, the 14 modified result can't be reached, meaning that the siege can't be won by the attacker, unless:
- It can assault,
- or it can starve the defender to death, thanks to the extra attrition (now that's working)!
Case study #3: Siege a forest province with not blockaded port with level 6 fortress
Attacker siege value = 0 (no leader, no cannons)
Defender siege value = 6 (fortress) + 2 (terrain) - P - D.
The initial modifier is -8, thus all your results will range from -7 to +2 and give you only extra attrition on attacker
.
With a +1 leader and lots of artillery (+3), your initial modifier will be -4, so a 60% chance of extra attrition on attacker, 20% change of nothing happening, and 20% of increase P by 1 and a 1% extra attrition on defenders...
In that situation, only time can help you and only if you are able to blockade the port (or if there is no port at all).
What are the siege parameters?
In the Siege information window:
- The number on the left is that attacker siege value
- The number on the right is the defender siege value.
How is the attacker siege value computed:
The attacker siege value is the addition of:
- The best siege capabilities among the attackers leaders
- An artillery bonus that depends on the number of artillery and the fortress level:
Fortress level ranges from 1 (minimal) to 6 (maximum).
If the number of artillery is greater than or equals to 40 * fortress level, artillery bonus is +3.
else if the number of artillery is greater than or equals to 25 * fortress level, artillery bonus is +2.
else if the number of artillery is greater than or equals to 10 * fortress level, artillery bonus is +1.
else the artillery bonus is 0.
How is the defender siege value computed:
The defender siege value is the addition of:
- The siege ranking of the fortress unit (I guess this is the default siege capabilities of the country's default leaders)
- The fortress level, from 1 to 6,
- The terrain modifier, which is 0 for plains and 2 for all other terrains,
Two other parameters are substracted to the defender siege value (causing it to become negative):
- A progress variable named P, ranging from 0 to 8 and representing successful offensive actions against the defenders
- A duration variable D, that grows over time (+0.3 per siege cycle, see below) if the city is not a not blockaded coastal province.
How does the siege evolves?
At the end of each siege cycle (usually once per month, although siege are faster during the Napoleonic land era), the siege evolves.
First, if the defender forces are reduced to less than 100 men, there is a great chance that they surrender.
Then, a randomly generated number, modified by both sides' siege values represents the siege progress:
Code:
[FONT=courier new]
Result = Random number from 1 to 10 + Attacker siege value - Defender Siege Value
Result <= 2 Attackers attrition +5%
3 <= Result <= 4 Nothing happens
5 <= Result <= 7 Food shortage, P = P+1, Defenders attrition +1%
8 <= Result <= 10 Water shortage, P = P+3, Defenders attrition +3%
11 <= Result <= 12 Breach: Breaches = Breaches + 1, P = P+2,
Result = 13 Dessertation: Defenders attrition +10%
14 <= Result Surrender!
Note: P can't be greater than 8.
[/FONT]Important note: Extra attrition will only be applied correctly in the next 1.06 patch.
Finally, the D parameter is updated. It represents the defender weariness, its lack of supply.
If the province has a not blockaded port, then D is decreased by 0.3 up to 0.
If the province has no port, or if its port is blockaded, then D is increased by 0.3.
What are the effect of breaches:
If there has been at least one breach, the fortress level is not substracted from the attackers shock & fire values during assault.
Case study #1: Siege a plain province with a level 1 fortress but no port, with a +1 siege leader on your side
Attacker siege value = 1 (+1 leader, no cannons)
Defender siege value = 1 (fortress) + 0 (terrain) - P - D.
D will increase by 0.3 each month.
P will increase over time to its maximum value of 8.
Initial modifier (P=0, D=0) = 0, modified result ranging from 1 to 10:
After 8 month, D = 3.2 (3), modifier is +3, modified result ranges from 4 to 14 even if P is still at 0 so you are able to win the siege (10% chance each turn).
Case study #2: Siege a forest province with a level 3 fortress and a not blockaded port, with no good siege leader on your side
Attacker siege value = 0 (no leader, no cannons)
Defender siege value = 3 (fortress) + 2 (terrain) - P - D.
As the province port is not blockaded, D will not increase and stays at 0.
P will increase over time to its maximum value of 8.
So the minimal defender siege value is -3. Whatever the random number is, the 14 modified result can't be reached, meaning that the siege can't be won by the attacker, unless:
- It can assault,
- or it can starve the defender to death, thanks to the extra attrition (now that's working)!
Case study #3: Siege a forest province with not blockaded port with level 6 fortress
Attacker siege value = 0 (no leader, no cannons)
Defender siege value = 6 (fortress) + 2 (terrain) - P - D.
The initial modifier is -8, thus all your results will range from -7 to +2 and give you only extra attrition on attacker
.With a +1 leader and lots of artillery (+3), your initial modifier will be -4, so a 60% chance of extra attrition on attacker, 20% change of nothing happening, and 20% of increase P by 1 and a 1% extra attrition on defenders...
In that situation, only time can help you and only if you are able to blockade the port (or if there is no port at all).
Last edited: