Defense is an important part of the game. Other players can attack you to cash in on your ready to collect gold, supplies, and goods. This can mean your many hours of waiting and spent gold/supplies for goods can be wasted. Another reason players attack each other is to gain points in each Age's PVP Tournament.
The better you understand how the AI (Artificial Intelligence) controls units for defense, the less you will lose and the better you will be attacking because all defense is AI controlled.
At the bottom we discuss specific units' defense strategies and why some work better than others. Note that any defense can be beaten by a smart human player with the same age of units. Generally, the first or second time if they predict how you will set your defenses.
"Invincibility lies in the defense; the possibility of victory in the attack." Sun Tzu
Since you don't control the defense units, there is actually no invincible defense. The goal of defense is not being unbeatable but for the enemy seeing your defense to surrender, or to do maximum damage to the attacking army. Then, even if they win against you, if they lost a lot of troops and only plundered some gold, they won't attack you next time.
- Terrain: The AI does seem to strategically use terrain to its advantage. Whether landing on advantageous terrain, or blocking your advantageous terrain, AIs don't seem to care.
- Movement: The AI will usually use its max allotted moves, while staying out of range of your attack.
- Targets: Generally, the AI will go out of its way to target your Rogues, then artillery then ranged units, even if it means the doom of the unit attacking it. Next, the AI proceeds to attack fast units then, light units and finally heavy units.
- Terrain: The AI will use the best terrain possible and will kill what it deems to be the best target. Its first choice is usually artillery units.
- Movement: The AI will, depending on the psychology of the situation, move 1/2 to full move. It will avoid a full move if it can not gain an advantage of damage dealt with that unit.
- Targets: The AI targets the unit of which the unit it is controlling will protect himself most. This almost always means going out of its way to forest, hills or rocks.
Overall, AIs make good decisions when defending; but the human brain can outsmart the AI during attacks by using strategies that enable the attacker to defeat the entire defending force while suffering minimal losses and damage.
Terrain: The AI can be tricked to land on terrain that puts it in a very bad situation if it deems it will be most effective in that spot regardless of if it makes your units most effective against it in that spot.
Movement: The AI will NEVER move away from you unless an obstacle is in its way. It will never retreat or surrender. It is a math machine. It wont move away from you because it thinks it is better to attack a heavy unit with a light unit than any other move moving it at least 1/2 its move to your units.
Targets: It will target the unit that it can do the most damage to even if it puts it in a bad placement which just happens to be your ranged units first. If the attacker is a heavy unit and AI is light unit it will avoid doing a max move just to take more or equal in retaliation damage as the initial attack. It will instead move 1/2 its move and stop. If 1/2 its move puts it in range of the heavy unit it will attack it if no better target. It deems that it will take massive damage the next turn from the heavy unit so doing some damage is better than possibly doing none or even less. This also means it will charge into a group of heavy units to attack a ranged unit. The reason is it says doing 7-8 damage to a ranged unit is better than doing 2-4 to a heavy unit and it wont be retaliated. This is unfortunately despite it probably taking 2-4 from the ranged unit on its turn and 5-6 from the heavy unit. So it does not take into account that on the next turn it did 8 damage but will take 10 from placement.
If the AI has a light unit and a ranged unit and Fast Unit are both in range it may look random which it will attack. At no age can a light unit 1 hit kill either so that is out as a deciding factor. The damage to both will be high so that makes it more complicated. It will see that the ranged unit cant retaliate and the Fast Unit can. Also it will note that the base ranged unit damage is always more than Fast Unit of the same age. There for it will target the one that will do the least retaliation damage and has the most potential for damage. This means once again the ranged unit gets the short end of the stick. This is a smart move and a human should do the same.
AI Controlled will target which: This is generally. Don't put it past the AI artillery units to kill your light units next to it instead of killing your ranged units on the other side of the map if it can preserve its own life.
Kiting: This strategy is present in many games mostly vs AI but some times vs human players. The word comes from flying a kite in the sky. There is a kite but it is controlled by a small strong string. The kite goes where ever the string directs it. You can kite the AI in this game. This makes having many ranged classes viable. Use a Fast Unit or a light unit as your string to kite the AI. Move it to top or bottom of the map and as forward as possible without getting with in range of their ranged unit s or melee classes. Then send your artillery units to the opposite corner of the map. Then send your ranged unit s to the opposite site of the map as the light unit but not quite as forward as the light unit. Every turn move the light unit back some but still out of range and keeping it the most forward unit. The AI will try to go for the most forward unit regardless of what it is. Then every turn you can move it back or when you can't do that any more move in the direction of your ranged classes but only move it as much as needed to keep out of AI reach. The AI will keep chasing it and all the while your artillery unit is pelting them and your ranged unit it cutting them down. If any of the AI break off to your ranged classes it should not be a big concern while you have several ranged classes to take them out.
The AI does a great job controlling them and is hard to mess up. Artillery units you can get away with having many of them. Some will do up to 8. It can work because artillery unit is the most reliable unit for the AI to control. With the range they are guaranteed to kill at least a few units. Even vs. 8 fast units they are guaranteed to kill some of them before they can reach them the 2nd turn and wipe out most of them. Artillery unit is hard to mess up even for the AI. They will not move them forward generally from their starting position. They may the first turn move them to get in range but less as ages progress and they get more range. If the enemy is getting close, the AI will move the artillery unit backwards or vertically but never forward. This is the only exception of a unit trying to retreat.
There is much discussion and controversy about how the AI controls artillery units. It is actually about how it controls the other units. When any artillery unit is used by the AI it will not charge as normal but instead switch to a defensive match. The other units will move generally 1/4-1/2 their move forward. Placing the heavy unit in front, directly behind is the light unit and directly behind that is the ranged unit. This is the only time the AI will actively try to protect units. Fast units will still charge off to seek and destroy ranged classes but at a slower move speed.
Controversy is that the AI changes its strategy for artillery units and no other units. Depending on if you want the AI to control your units this way many people just won’t use any artillery units on defense.
It does an ok job at controlling them but especially early game it can be a problem. Until the heavy unit have more move than ranged units your ranged units will consistently be moved ahead of the heavy unit who are to protect them. This consistently causes your ranged units to be plowed down by the first unit to reach them with the heavy unit standing behind them. Avoid this by placing less ranged units than you would use if attacking with that group. Because of this you want at least equal amounts of ranged units to light/heavy units to protect them. If you opt for more light units than heavy units this suicide can be partially negated. Some will opt for many ranged units over the suggested 4. If done you MUST use light units as their support unit. You can have to many since they don't retaliate. They do so much damage and are still generally good that you should always consider using some for defense.
It does a very good job controlling them. They have the highest total attack/defense of any units except rangers. This makes them very hard for the AI to completely mess up. Also their terrain of plains is extremely common and gives a fair chance to randomly land on them to its advantage. You don't want to have too many. They can be easy prey for human controlled ranged classes. They are such a high attack/defense it is hard to go wrong with having 1 heavy unit. It is also a good idea to use heavy units against many light units. Using 3-4 of these units, and one or two fast units to destroy the ranged units is a good idea.
Does ok at controlling them. The reason why not ranked as well as heavy unit is their stats aren't quite as good and the chances of them landing on bush/forest is pretty bad. A human controlled light units can be nearly as tough as a heavy unit but not with the AI. They are still good for countering fast units and moving ahead of ranged units indirectly protecting them. Their speed is great at closing the gap to get to ranged classes. You can definitely have to many as the AI is less than awesome with them and since heavy unit is so common. They are still very good units and with their speed it is hard to go wrong with them but you may occasionally not use any in favor of heavy units or late game fast units.
The AI is worst with fast units than all its other unit mistakes combined! The AI as described above can be without much trouble tricked into being close to a non ranged class and not being able to reach a ranged class so it will instead attack a melee class. This is because it will never retreat a fast unit. A human controlled fast unit will be retreated and re-maneuvered possibly several times until you can get in the position you want to take out a ranged class. AI controlling 4 fast units with a human controlling 4 ranged classes are still not a threat to the ranged classes. It will mean spending a few turns retreating to a corner and killing the fast when they decide to charge your melee classes. AI often wastes them and you would be better off just adding more light units instead. Ranged classes are commonly used so it would not be the worst thing to have a few fast units but don't count on them being super effective. Bronze/iron age fast units are sub par at best and should not even be considered to use for defense. Early/high middle ages are decent and you may decide to use them. Late middle ages/colonial age are on par with heavy/light units and should be considered to be used but sparingly. This will make a difference on deciding to use them or not.
Wall of Rain:
Units: 3-4 heavy units, 3-4 ranged units, 0-1 artillery units, 0-2 light units, 0 fast units
This is a very strong defense. It is, as any, beatable by a decent player. Your weaknesses are fast units but the heavy units will do ok at countering them and ranged classes but your ranged units will do ok at countering other ranged classes. You can substitute a ranged for a artillery unit for the AI to better pick off their ranged classes threatening your heavy units. Light unit is so hard to go wrong with they can again counter fast and close the gap to kill their ranged classes. This does well but can be countered as it is more specialized in mostly 2 units.
Together we stand divided we fall
Units: 1-3 artillery units, 1-3 ranged units, 1-3 heavy units, 1-3 light units, 0-2 fast units
Having 2 of each non fast unit is not a bad idea. Generally having 4 melee classes/4 ranged classes are a pretty balanced force. You can decide to have more or less of other but must have 4:4 ratio. Replacing range with other range is ok but still have at least 1 of each. Same for light/heavy units. Mid-late game you can use fast units but have it come from the melee class pool and change it to 5 melee classes/ 3 ranged classes. This category in general is very strong being so versatile and knowing they cant just break it by picking the counter units to each of yours. Which would be 4 fast units, 2 ranged classes and 2 heavy units.
8 of a kind
Units: 8 of any 1 unit type
Some swear by this formation and some hate it. The ones sworn by are all long range or all short range.
All artillery units you are guaranteed to take out a few units before even a fast units can reach you, which will dominate you 2nd turn.
All ranged units not quite as all or nothing but still vulnerable to fast units and may not get that automatic kills if they hold off their fast units right but should still get many kills.
All heavy units are moderately slow so it could get dominated by ranged classes. If they are heavy units it will do very well.
All light units are moderately fast but not as tough as heavy units. It will at least do ok. They will quickly hunt down their ranged classes and start costing them a lot of money to replace them.
All fast units are probably the worst defense of any combination of 8 units you could do. They can be easily tricked to waste attacks on melee classes and be thus dominated by them. All this while their ranged classes survived and are pelting them.
All formations used should be based off of 1 of these 3. Either you have 2 units in large numbers, you have many units in few numbers or all of 1 unit. The few of many is very versatile and will be the most likely not to outright lose as much. The all of 1 type is an all or nothing. Either it does very well in the match up or its a disaster, its a gamble. Many of a few units is more versatile than 8 of a kind but suffers the same problems of 8 of a kind. Either it does pretty well or gets countered.