Infantry comes in many forms and strengths. This section deals only with melee infantry, missile troops are described in a separate section. I will try to describe the most commonly featured types of infantry first and then address various basic tactics.
Swordsmen, Macemen and other one handed weapons except spears
Featuring everything from barely dressed tribesmen to the walking cans known as dismounted knights, these troops are mainly for use against other infantry. They usually have high defence deriving from the shield combined with armour and/or defence skill. They are ineffective against cavalry compared to other infantry. Armour piercing axes and maces generally have an edge over swords later in the game as more and more protection derives from armour rather than skill.
The basic anti-cavalry infantry, ranging from the puny spear militia to magnificent guard units. The spears have a bonus against riders but generally lower attack than other infantry weapons. Most spearmen carry huge shields, although a general lack of armour make most rather vulnerable to arrows anyway. Spearmen are generally useful for holding a line against both infantry and cavalry. Most are too weak to do well one on one against heavy cavalry, at least in open terrain.
Two handed swords and axes
With a generally higher attack and charge than other infantry, most of these units have a lower defence. In many mods they also have a bonus against cavalry. They are however among the most vulnerable to a cavalry charge and to missiles. As armour increases in the game, this infantry is gradually gaining on other infantry. In most mods they are effective against pikemen.
Pikemen and halberdiers
Generally appearing late in the game, these troops have fantastic defence abilities due to the long reach of the weapons and the phalanx/spear wall formation. They can keep much infantry and cavalry away from them in guard mode for quite some time. Pikemen have generally longer weapons and higher bonus against cavalry. Halberdiers often have better defence and pierces armour. Both can stop cavalry better than other infantry, but pikemen do it best. Halberdiers are generally better at killing the cavalry once they have stopped. Both are notoriously vulnerable to missiles since they lack shields and move slowly.
Some units like the janissary heavy infantry are armed with a halberd yet do not form phalanxes nor move slowly. They also charge decently. Their weapons works mostly like a two handed axe but seem to have increased range and better ability to stop cavalry when they brace. I have played with, and looked at these very little so I can’t say for sure.
The strength of infantry is its numbers and constant effectiveness, in the way that they do not depend on a high charge or good view of the enemy. Infantry fights well everywhere but thrive in settlements and woods since it protects against cavalry and missiles. The disadvantages are lack of speed and individual weakness, thereby being dependant on good order and cooperation between units. The infantry is usually relatively stationary in field battles, making up the centre and engaging enemy counterparts. As the game progresses they can fill a more and more active role as more advanced troops become available. Some factions posses’ strong and diverse infantry right from the start.
2.2 Resisting cavalry early in the game
My definition of early is before strong phalanx units appear that can stop cavalry in its tracks all alone. The only troops in that time that are good at absorbing a charge are usually spearmen. Spearmen are defensive infantry and work best when standing still and bracing. If you look at a unit of those you will see that they at first stand idle and relax, then, when the enemy closes, they raise their shields and spears to form a wall. That is when they become effective. I don’t know exactly but my guess is that some of their bonuses are tied to this bracing animation. Spearmen on the move who are hit are very vulnerable in comparison.
First of all, you would want to make enemy charges as ineffective as possible. That can be done in a number of ways which all aim to reduce the number of riders that hit your men with their lance. There are often natural obstacles to take advantage of. Trees work great, bigger rocks can help also. If you fight close to settlements there is often a building or two. Buildings can be used to guard a flank or frontally to disrupt the enemy formation. Position your infantry a little behind a building and the foes cavalry will have to use a narrow space which means that riders will get in the way of each other.
If you don’t have natural obstacles, there may be some cultural ones available. Siege units are actually a great asset in the field even when they cannot fire. Positioned in front of infantry they can block a big part of the passage, restricting cavalry to using narrow passages between them. More about these tactics below. Trebuchets and mangonels are often the best because of their size but take the number of artillery pieces per unit into account as well.
Another way to reduce the impact is to make the target as small as possible. Forming schiltrom reduces the number of spearmen hit but also the number of riders being harmed by the spears. The same goes for all squares without supported flanks. Another option is to form a wedge of two units, pointing against the enemy. The wedge can hardly be hit frontally by more than one unit and the length of the formation makes it hard to outflank. The wedge will also be discussed in detail later.
If you lack spearmen or similar infantry, run. Not away from battle, but to the side, try to escape the charge as much as possible. Run away from a line of obstacles to let the cavalry be trapped and disorganised, then back to attack them while their formation is stretched out and vulnerable. If you have much offensive infantry, like two handed axemen, you may be able to flank a cavalry unit chasing one of the infantry. Try to position your units so that cavalry units get in the way of each other and to surround them so they cannot retreat to charge again.
2.3 Countering the cavalry early in the game
Supposing you defend with spearmen, you will likely need a more offensive unit to complement them; otherwise the enemy will be stopped but not very damaged. Among the infantry, two handed weapons are good at this. They can rush in fast and deal huge damage with their large weapons. To maximise this cooperation it is a good idea to leave gaps in the line of spearmen, where the offensive infantry can rush in. They can of course go through the spear formation but it takes time and the cavalry may escape. There is also a chance that cavalry charges into the gaps, enabling you to trap them. Spearmen can also be used in offensive manner but they may need to be ready to absorb another charge and it takes some time to reform the lines.
Once the cavalry retreats to charge again – which it typically will – you have the choice of following them to prevent them from charging again, or to reform your lines and await the next attack. Which option to chose depend on your troops (high proportion of offensive infantry or defensive) and on the battle as a whole. Perhaps you hold a very sound position or you need to check the cavalry to prevent them from attacking other more vulnerable troops. As the cavalry withdraw, it becomes a good target for missile troops, well worth a shot or two because their backs will be exposed.
2.4 Fighting cavalry late in the game
With the pikemen and elite spearmen becoming available later in the game your infantry can feel much safer. With pikemen it is absolutely vital that they absorb the charge in phalanx formation (have them stand still with guard mode and spear wall activated to make them form up) and are not flanked. Once they have been hit, deactivate guard mode to make them attack more and deal damage. Also send some offensive infantry or halberdiers forward to assist. Because pikes offer such good protection, other infantry can wait close to the front among the pikemen without much danger of being trampled.
Other than this, the same basics as before apply. Pikemen should not be overestimated and late cavalry can have tons of armour. Use everything at hand to block their charge. If you make a square of spearmen or pikemen make sure the corners overlap each other. Although soldiers on the flanks sometimes turn to brace against flanking enemies the line as a whole will not do well when being flanked.
2.5 Fighting infantry
Actually all infantry can be good at something versus enemy infantry. Spearmen and pikemen are usually ineffective, but can at least hold the line for a while. Swordsmen excel at it and two-hander’s are good at flanking where they may spread out and to crack armour.
Because pikemen can use the weapons of several of their ranks they are good at supporting other infantry. For example: positioning swordsmen with the first rank just before the first rank of pikemen combines the high defence of the swordsmen with the support and cavalry protection of the pikemen. The most extreme version of this that I know is probably to place gunners at the first rank. In one battle the enemy infantry (dismounted knights if I remember correctly) were unable to get past the pikes, which allowed for the gunners to reload and fire, routing them. Pikemen can also be good at attacking a small portion of the enemy front, where they can outnumber the enemy by being able to bring more weapons to bear (like in the battle of Leuctra in Greece between Sparta and Thebes). Overall they are effective against crowds of enemies like many engaged units in field battles and on crowded city streets. Always support them to keep their flank protected and counter anti-pike units if such exist.
More or less the same things apply here as for pikemen. Halberdiers are generally better against infantry than pikemen are, with more armour and attack. They are less effective as support units since they have shorter weapons.
…with swordsmen and their like
Easily the strongest overall, swordsmen can be used in many ways. They can defend or attack with equal ability and flank as well as penetrate. Their weakness is the short reach of the weapons which sometimes let spearmen and phalanx units keep them at a distance. Because they have generally high defence, they are very good at exhausting the enemy – holding the line for a long time, seeking to make as many enemy units as possible engage and tire rather than going offensive.
…with two-handed swords and axes
These troops can be rather different depending on what mod you play. Mostly, because of the slow attack speed, they do well in open areas where fewer enemies interrupt the attack. With good armour they can be very effective since it compensates for their lack of shield and defence skill. They are often very ineffective in crowded areas like when storming a gate or across a bridge, especially early less armoured versions. A good way to use them in the field is often to allow a more defensive unit to engage the foe and then send two-handers at their flank or at a gap in your line. Their charge can make it worth the time to position them well before striking, as with cavalry. In some mods they are especially good against pikemen.
Against enemy infantry there is much less need to use obstacles and other ways to disrupt their attack. Depending on your strategy you may benefit greatly from these though. Higher ground is also great because infantry move slower and tire quicker than cavalry. First, decide if you want to defend or attack. By this I mean that when you engage the enemy foot soldiers, whether you come to them or they come to you, there are several ways of continuing.
The complete defending is to simply hold the ground until enemies rout from exhaustion or some other troops can make an attack. Here is a situation where obstacles are very important. Your goal will be to engage as many enemy units as possible, with as few of your own and as little effort as possible. It is a good start to make the foe get in the way of each other and be stopped in bottleneck situations. That will reduce the number of soldiers who actually fight and do damage, but their whole unit will still be fatigued. The reduced intensity also means that you can use guard mode (see above) without risking great casualties. Using guard mode further helps conserving the strength of your men. Defensive units are of course best for this kind of tactic. Stretch out their lines as far as you can without risking a breakthrough in order to make them “catch” as many enemies as possible. Using a circular or pointed formation is often good for this, because the ai seems to have trouble with spreading out units properly, thus letting them get in the way of each other.
Flanking the enemy is pretty much the same as with cavalry. The most notable differences are the weaker charge and slower speed of infantry. When you send infantry around an enemy flank, make sure they are formed up properly before striking the enemy side or rear. Infantry do not crash into other infantry like riders do, so they need a wide line in order to be effective and not have the majority of the soldiers forming deep but useless ranks. There are of course situations where a compact formation is desirable, like when you want to maintain mobility or in order to fend off cavalry. Because infantry cannot withdraw quickly, it is often best to send more than one flanking unit around. Then one unit can attack the enemy infantry and the other can cover its back against enemy reinforcements.
Penetrating the enemy line is a manoeuvre where infantry can really shine. This way of attacking is usually associated with cavalry who are also good at it. However, when the cavalry get stuck among enemy troops they are very ineffective, but infantry handles that rather well. In the game the armies are small and one unit can get from one flank to another or to the centre in no time, making it very hard to penetrate the line and avoid being caught up by enemy reinforcements. Therefore infantry is good since it doesn’t suffer from stopping. The force used for this kind of attack needs both good anti-infantry units and preferably something that can deal with cavalry rushing in to reinforce the enemy line and dispose of generals bodyguards (who are often the main target of the attack). In these cramped situations pikemen and halberdiers work great, but watch their vulnerable flanks in the disordered melee. Two-handed weapons may have difficulties in the tightly packed formations but being effective against both riders and foot soldiers is a great asset, especially since the mass of enemy infantry surrounding the penetrating force will stop cavalry charges from reaching them.
If you want to stand your ground but still use offensive infantry to great effect it is a good idea to have open areas in the line of spearmen or whoever is holding it. Both a lot of smaller gaps (like against cavalry, see section 2.3) or a few larger can be effective. Leaving a large gap allow you to lure enemy infantry into it and envelop it almost completely. The enveloped enemies will have much space around them, allowing your two-handers to be very effective.
Example: Enemy infantry (E) deploys in a usual thick line. Allied spearmen and swordsmen (S) form a line with a large hole where offensive infantry (O) wait to strike (1). Both lines engage and the enemy infantry pour into the hole which is large enough to let them pass. Friendly reinforcements form compact formations to be ready to defend the flanks of the friendly first line and to cut off the penetrating enemy unit. The offensive infantry spread out to attack effectively (2). Both sides suffer casualties in the first line where units are reduced to three in each. Allied reinforcing S move in between the two penetrating enemy units and cut off the first of them while the offensive infantry attack from two sides and almost envelop it. One enemy unit is completely enveloped and will have at least one two-hander striking at its back. The second enemy unit is prevented from exploiting its breakthrough by flanking your first line.
The principle here is to penetrate the enemy lines to cut off a smaller part of the enemy army and then use local numerical superiority to quickly destroy it while keeping the rest of the enemy occupied. This can be done in many more ways and both cavalry, infantry and missile troops can find a way to make themselves useful for it.