Originally Posted by
Jurand of Cracow
1. CAI is absolutely broken on the choice what to defend. Usually, it leaves the main settlement empty, concentrating troops in a fort present in the province. Or it moves it between them. A player can easily exploit this behavior.
2. However, the AI doesn’t know how to use forts strategically in the way the player does. It doesn't use the forts to block the player's advances to buy time for the reserves to come. It also leaves forts from time to time (it doesn't stay in a fort, it moves out and in - if it's a temporary fort then it disappears).
3. While on the offensive, the AI sieges a fort instead of the settlement, furthermore it breaks these sieges very often. The result is: a player can dupe the AI easily into endless sieges.
4. The number of siege battles is high with the permanent forts. The chrome of the forts is nice, but it's a nightmare to play with: you're bogged down in dozens of irrelevant sieges.
5. Western Europe is already full of settlements close to one another, so any forts would limit the tactical movements even more, with the player blocking passes through the mountains or woods. The result would be a restricted tactical movement, detrimental to the AI as it's not really capable of assessing the situation and sending troops around, or not sending them.
x) If the buildable forts are additionally related with the free_upkeep then an exploit is possible: you farm the forts to keep your whole army without paying upkeep (it was the case of the HURB, but also in the DLV).