A siege is a type of military action intended to capture a fortified city. Sieges are initiated automatically whenever there are a sufficient number of non-moving troops in a province with an enemy-controlled city. Assuming enough troops are present, sieges may progress once each month. When a siege has sufficiently progressed, capture of the city becomes possible.
Requirements to Siege
To siege a city, it must be enemy-controlled, and there must be enough non-moving troops present to siege. The amount required is 5 army units per level of the fortifications.
Fort level Army units required to siege 1 5 2 10 3 15 4 20 5 25 6 30
For example, a force of 2000 infantry and 30 cannon is sufficient to siege a level 1 fort.
When you have sufficient force present, siege is automatically initiated. The force initiating the siege is called the siege force or siege attacker. Forces in the city (otherwise never shown) become the siege defenders.
Once a siege has been initiated by a force, so long as at least a cover force is left in the province, the siege is not ended and siege progress will be computed.
Although many countries may have forces present at a siege, only one controls the siege. Control of a siege determines which country will end up occupying the city, assuming that the siege captures the city.
There are several factors which determine who controls a siege, when multiple countries are present. Here they are listed in order of priority:
- rank -- the highest ranking leader present controls the siege.
- time of arrival -- if the leaders are the same, then the siege is controlled by the country which owns the first army to arrive in the province except for a bizzare twist for Venice.
There is no way in the game to see the time of arrival. Note that when you split an army at a siege, its time of arrival does not change. However, the newly created army split from it "arrives" after everyone else. So, it's very easy to lose control of a siege this way. Typically, you've got a force sieging then you notice an allied AI has moved in a huge army to "help", which will cause huge attrition to you. So you split your siege force via the "cover" button, and move away. Woops! Lost the siege.
When you split an army using "cover", the cover force -- the small bit -- is the newly created piece. Thus, it may be moved away safely, but the large part may not. If you want to move away most of an army, you must click "cover" repeatedly, then move away all the small bits. Similarly, when you hit the "siege" button, the siege force (on a minimal fort, the bit with 6000 men) is the newly created piece. In both cases, Paradox implemented things backwards. I recommend always saving immediately before you try to flee an AI-dogpile siege, so that if you screw up moving away and lose the siege, you can just reload.
On the main map, the game shows a little cannon icon firing when you initiate siege. A force that is sieging is shown with the cannon icon, and the cannon fires each time that siege progress is checked. The flag that is topmost among the sieging forces is the flag of the country controlling the siege. The progress of the siege is shown as a bar under the sieging force; the color of the bar goes from green down to yellow down to red as the siege progresses.
When you select a siege army, or a city you own and control if it is being sieged, you get the siege screen. The siege screen shows the siege attacker and defender, with the attacker on the left, and defender on the right. The attacker's coat of arms is that of the siege controller. A number is shown for each party: on the left, the attacker's siege value; on the right, the defender's siege value.
The city depicted in the siege screen shows the progress value P (see below), with one fire shown per P level. Breaches in the walls are also shown.
The attacker's siege value is zero by default, but two bonuses are possible based on the attacking units present at the siege. The siege value of the leader with the best siege value is added. A bonus from +1 to +3 may apply if enough artillery are present. The artillery bonus depends on the number of artillery (#A) and the fortification level (F) of the city.
- +3 if #A >= 40*F
- +2 if #A >= 25*F
- +1 if #A >= 10*F
For example, if you have 20 cannon present at a siege of a small fortress (level 2), you get a +1 bonus to your siege value. 49 cannon get the same +1, but 50 get +2.
The attacker's siege value does not change during the siege, except insofar as the attacker moves away or loses leaders or artillery.
The defender's siege value starts as the fortress level (from 1 to 6), with two bonuses possible:
- +1 if the country has its Offensive domestic policy slider at 0 or 1.
- +2 if the terrain in the province is anything except plains.
Unlike the attacker's number, the defender's number evolves with the siege, gradually going lower as siege progress is made.
Siege evolution is tracked internally by four parameters.
- #defenders, which starts at 5000 times the fort level
- A "progress" variable (P), which ranges from 0 to 8.
- A "duration" variable (D), which grows based on time of siege.
- A "breach" variable, representing whether one or more breaches have been made in the walls.
Progress and duration both are subtracted from the defender's siege value.
Initially the #defenders is 5000 times the fort level. Both P and D are zero, and there are no breaches.
Every 30 days after a siege is initiated, the siege evolves. (Exception: during the Napoleonic land era, siege evolution happens more often.) A random number from 1 to 10 is generated; the attacker's siege value is added, and the defender's is subtracted. This gives a number, N. The result can be found on this table:
N Result ----- --------------- 4 or less Nothing happens. 5,6,7 P = P+1, Defenders attrit 1% 8,9,10 P = P+3, Defenders attrit 3% 11,12 P = P+2, Breaches = true 13 Defenders attrit 10% 14+ City captured
Breaches are visible on the siege screen, as flaming gaps in the walls. (One or two breaches may be shown; there's no difference between one and two except this display.) Breaches do not affect sieges per se; breaches only affect assaults. (Unless there is breach, the fortress level is subtracted from the attacker's shock and fire values during assaults.)
The number of defenders, like breaches, only matters in an assault. You can watch their numbers dwindle on the siege screen, on the Garrison side.
Assuming the city has not been captured, the D variable is updated. Usually, it goes up by 0.3. The exception is when the city has a port and the port is not blockaded, in which case, D decreases by 0.3 down to a minimum of 0. (There is no upper limit to D.)
Finally, a new check is made of the requirements to siege, exactly as if the forces had just entered the province.
Siege State Reset
A city's status is checked at each month end. If the city is neither covered or sieged, and there is no battle in the province, then all of its siege variables are reset to their initial state. Otherwise,
This is the only way in which the siege state is reset. Here's some of the implications:
- You can leave a siege indefinitely with a cover force and you won't lose your progress.
- You can leave a siege, then return to it in the same month without losing progress. This is generally not a good idea, because the enemy may build troops as soon as the province is not covered. However, if what you want is warscore, and you've got a siege in the plains where the enemy cannot build many troops and a nice large cavalry army there...
- If a siege force is defeated in battle, that won't reset the siege. It is quite possible to take over an advanced siege from an enemy siege-force (usually from rebels) by beating them in battle.
- If the siege force captures the city, it does not reset the siege. It can be useful in certain cases to arrange for the siege progress day to be on the first of a month, in order to have a full month available to re-siege a captured city. (Exploits are left as an exercise to the reader.)
Another way in which siege reset can be used by a player is in dealing with "nationalist" rebellions. See the article on How to Handle Rebels.