The Shape of Your Castle
I wrote this article to add some information to what NAT wrote in his article, "Art of the Defensive Siege", as I've found that the shape of the castle is also of great importance in defense. Not only will a badly designed castle represent a big disadvantage, but some "architectural" tricks might make the difference between losing and winning a game.
There are 2 types of tricks you can use:
1. Tricks based on the faults of the AI
2. Tricks based on general game rules (or properties)
I. Errors in the way the enemy "thinks"
The enemy melee troops always choose the shortest way to your king. You can use this to your advantage. If you think you know the way the troops will go after smashing the walls, you can prepare the ground for their arrival. There are plenty of things you can do: setting traps and pitch in the way is efficient, but takes a lot of resources and you can't replace them by new ones after they are triggered / set on fire if there are enemies nearby. Engineers with oil or fire throwers (in Crusader) can be quite useful.
The enemy melee troops won't destroy stairs while sitting on them. That allows you to create in Stronghold what you never thought could be built: an invincible wall. To do that, you have to build a normal wall (preferably a low wall if you are playing Crusader) and then you have to build stairways facing the enemy. It is important not to let the troops make contact with the wall. Take the following screenshot from my "J_Jester" map as an example.
At first, the AI attacks with moat diggers. It is a good idea to aim to preserve the moat. In "ultimatum-castle in the woods" map I redistributed the troops. I sent 80% of the troops at the front wall, the one facing the enemy, and 10% on each of the lateral sides. I used the pitch for big groups and, during the attacks, filled the small holes in the moat with pitch so that no troops reach the walls. I didn't manage that. I had to take 5 archers out of the castle and cover with water the 3 places where the pikemen reached the walls. After doing that, all the swordsmen were practice targets for my archers. (The picture shows that after having killed all the moat diggers I still had my moat intact.)
When you set pitch on fire, enemy troops will try to avoid the flames. When you have a hole in the walls all the troops will squeeze themselves through. But what if you have an opening in the walls and the ground is set on fire? Do you think troops won't pass? Wrong!!! Totally wrong!!! They will go through the opening like sheep. From this moment you have to quit thinking like "all castles should be enclosed" or "it is too risky". Remember the first trick: Melee troops will choose the shortest way to your king so, if your castle isn't enclosed you won't have to build thick walls and moats. The situation is different if you are attacked with siege equipment. You are not finished yet. Some troops might still escape the flames so you will have to maximize the effect of the flames by keeping the enemy troops on fire for a longer time. Here is what I have in mind (you can replace fire throwers with engineers if you are not playing Crusader.)
II. The tricks I showed you until now are based on the fact that the "game intelligence" is... well... doesn't exist at all. The following are meant to show you that it can sometimes help you.
Your ranged troops attack other ranged troops first. This is in your advantage if you have a good way of managing the problem with enemy melee troops like the last one. This doesn't help you at all if you are attacked with archers and digger units at the same time and you're trying to keep your moat intact.
When they made this game, they didn't want swordsmen to attack isolated wall segments. They made melee troops avoid unnecessary efforts. That is why if you build a small tower outside your castle and a gatehouse to get archers on top, enemy melee troops will ignore the tower and head to the walls that enclose the keep. That will give you a great advantage, for it will allow you to start firing earlier.
This is also THE BEST DEFENCE THERE IS AGAINST SEIGE EQUIPMENT because when engineers build catapults, rams, etc. they do it away from your castle walls but not far away from your outpost.
Like I said earlier, all enemy troops avoid attacking isolated wall segments, right? Wrong! I only said that melee troops do that. You can use the fact that tunnelers dig their tunnels towards the closest wall or tower possible to your advantage. If you don't have a moat (the best defense there is against them) build a few wall segments close to your walls and see what happens
It is good to keep the enemy troops under your archers' fire for a longer time. Lord Thingol, when he built his "The Stronghold of Veron" map, used the following trick to keep the enemy away from his gatehouse:
It was well-intended, but there's another important consideration: What happens when you want to get out of the castle fast? I have a better solution for delaying melee troops and rams:
So, it is obvious that most of the tricks are based on delaying melee troops and keeping them under fire for a longer time. Here are some other screenshots of games in which I've used this tactic: The first one is from the Crusader Trail. Notice the fact that the castle isn't enclosed. The enemy can still try to enter the castle by climbing the long stairway in the upper-right corner, but then they would have to cross the long low wall while under heavy fire from the crossbowmen.
After finishing with the normal custom games I decided to build myself an ultimate mission: me against 7 allied Lionhearts, with equal resources. It took me several tries, but finally I discovered a way to complete it. I used some of the tricks above and more. Notice the fire ballistas behind the moat, the 2 outposts, the absence of walls, and the fact that I had no keep enclosure.