Originally Posted by
Strengelicher
There are several ways to deal with your problem.
1. You can lure them to sally out. To do this, the AI must regard your besieging army as inferior to the garrison. Obviously, this will probably not work if the ratio is 2:1 in your favour. Take only your strongest field units (preferably cavalry (missile and heavy)). The defenders will sally out during the first turn of the siege, as has been said above. Withdraw your men to lure them out further into the field. Then smash them with cavalry charges from all sides or whittle them down with missile units.
2. You can also lure them out by attacking an army of theirs stationed right next to a settlement. The garrison will sally out to help their comrades as long as the settlement is not besieged. Sometimes you can provoke a situation like the aforesaid like this: First, besiege a settlement. Second, attack a small enemy force nearby and beat them. They will try to withdraw into the settlement, but since it is besieged will stop right next to it. Third: Lift the siege and attack the adjacent army, the garrison will sally out to help. Please note that you need to completely destroy both armies in the field and kill any prisoners to prevent the survivors from fleeing back into the settlement after the battle.