Army Composition against the AI: Build Order Wins

The purpose of this guide is to explain how to secure a build order win. A build order win is achieved when the army that you field almost cannot lose against the army that your opponent fields. An army of heavy spearmen, for example, is virtually invincible against an army of medium melee cavalry. Most armies, however, are not that homogenous, and thus no army composed of only one unit type is likely to be successful in every situation. There are essentially two main army compositions that will counter ninety percent of AI controlled armies, even at the higher difficulties without exceptionally good control. The remaining handful of situations must be dealt with on a case-by-case basis: this guide will endeavor merely to summarize the dominant techniques I have used in the majority of situations.

The armies fielded by Western Enemies will usually be composed largely of melee infantry with smaller sections of ranged infantry, melee cavalry (by which I mean melee and shock), ranged cavalry, and artillery. The key to securing a build order win is arriving at the battlefield with more and/or superior heavy infantry. Every faction has a high end heavy infantry unit which is comparable to that of the other factions, such as Gallic Oathsworn or Roman Praetorians. This unit will form the core of most of your armies. Of course there are a few problems with this: these heavy infantry units are expensive, they are not immediately available, and they are not immediately better than those fielded by your rivals. The economic question is beyond the scope of this guide, but I will try to answer the other two problems here:

How do you win heavy infantry battles when each faction's heavy infantry is comparable?
There are four main ways to buff your vanilla heavy infantry into killing machines. The first is equipment. Capturing two iron producing regions will allow the construction of a shieldmaker and a swordsmith which combined will buff the melee attack and defense of every new unit and existing upgraded unit by 20% at maximum level. A unit dealing damage 20% faster and taking damage 20% slower than a comparable enemy unit will entirely kill an enemy unit with only 2/3 casualties assuming both units fight to the death.

The second way is through buildings which increase the melee attack and defense of units upon recruitment. Every faction has a training field type building which increases stat line on recruitment but the building available to barbarians is substantially better than that available to "civilized" factions. The barbarian building offers another +20% to melee attack and defense at max level in addition to money, while the civilized building gives +10% to either melee attack or defense. Barbarian tribes should immediately start setting up a recruitment province with all three recruitment buildings (cavalry, infantry, ranged troops), while the civilized factions should attempt to conquer one of the barbarian buildings and then turn that province into their recruitment region.

The third way is through training with a warlord or champion unit. Players should get champion units as fast as possible and attach them to armies to slowly boost unit experience. Choosing champions with an experience boosting trait is wise, and choosing zeal followed by warfare as skills will open up the main experience boosting trait which should be leveled as often as possible. As an additional benefit, high zeal champions can be detached from the army at crucial times to attack the patrols of an enemy army, inflicting casualties and limiting its movement speed.

The fourth way is through researching technologies which boost the combat stats of your units. This is the least important way as often economic research is more important to make sure that you can field the expensive top tier infantry units, but unlocking higher tier recruitment buildings should be a reasonably high priority. The third level infantry recuitment building should be one of your first researches.

I've got my heavy infantry. now what?
Once you have ten units of heavy swordsman and another couple units of heavy spearman, you can add on cavalry and light troops. I like to get four units of heavy cavalry (including my general) and three of archers. I often get a unit of onagers or ballistas as the final unit. Avoid heavy ballistas because they are immobile, but if you have the money and tech, heavy onagers are fine. In battle, form your swordsmen into a main line with the spearmen a few feet behind on the flanks. The archers and siege engines can deploy behind the army. I recommend turning off skirmish mode because otherwise your archers are liable to run away from their heavy infantry support. The cavalry, including the general, I usually deploy on the wings, two units to each wing. In battle, your siege equipment will usually induce the AI to attack, allowing you to hold formation. Your upgraded and trained heavy infantry should make short work of attacking infantry, while your cavalry first dispose of enemy melee cavalry and then circle around to dispose of enemy ranged infantry. The spearmen should be held back and used to intercept flanking cavalry units. The only time that you will have to make a dramatic move is when the enemy deploys several units of siege equipment. Then the heavy cavalry will have to prioritize killing the siege equipment as it will rapdily obliterate heavy infantry because in Rome II there is no loose formation toggle. One technique is to deploy your army at the back of the deployment box with cavalry hidden forward and to one side in the woods. Once the enemy heavy troops pass your cavalry, it can spring from hiding to kill the enemy siege engines.

The Problem
While heavy infantry is the key to defeating the melee infantry heavy western armies, eastern factions field much more ranged infantry and in the case of the nomadic factions, ranged cavalry. These units will easily outrun your heavy infantry while dealing heavy casualties. While the heavy infantry army may still prove successful if its cavalry is used to maximum effectiveness or in favorable situations such as river crossings, casualties will be unacceptably high.

The Solution
The eastern army does not field much quality infantry: most of the melee infantry will likely be hillman or eastern spearmen, both of which are all but worthless. Similarly, the eastern army employs very few armoured units. The lack of heavy infantry and armored units means that ranged infantry are very effective against the light eastern compositions. To hold the center of the line against an eastern army, 8 spear units should be sufficient. Ideally they should be heavy but not necessarily super heavy. Chosen spearmen would be completely adequate for example and thus spear nobles would probably be unnecessary. Your spearman exist to keep the enemy cavalry from overwhelming your ranged troops and to prevent the enemy melee infantry from chasing your ranged infantry and thus they are not the real killers of the army. They are a holding force and nothing more.

The exception is thureos spears. If you have access to thureos spears you should employ no fewer than 8 units and perhaps more. Thureos spears have a bonus against large and thus fight well against enemy cavalry and are adequate to kill light melee infantry. Furthermore they have the ranged attack of a javelin armed unit, which allows them to fight enemy skirmishers successfully, although they are not entirely effective against slingers and archers. Against horse archers, thureos spears are nothing short of lethal as the enemy horsemen will usually ride within range and will be severely worsted in the subsequent missile exchange due to their lesser numbers and lighter armour.

Ranged troops will form much of the rest of the army. I prefer archers over slingers anbd javelinmen because archers have the range to engage enemy slingers and archers and the arc of fire to remain behind your spearmen. Slingers, on the other hand, will kill many of your spearmen from behind. Eight units of archers will be able to put down a withering fire on enemy missile troops, particularly ranged cavalry, and rout them in one or two volleys if focus fired well. Again I recommend having one unit of siege equipment, usually ballistas, to force the enemy toward you, and to inflict massive casualties on bunched units, particularly cavalry.

The final section of your army should be 3-4 units of cavalry. Unlike in the west, the heaviest cavalry available to you may not be the best, and you may be better off employing heavy melee cavalry as opposed to very heavy. As far as mercenaries go, both cappadocian cavalry and persian cavalry are very respectable.

Controlling your army in battle
The deployment of your army will be much the same as the western army, with six units of spearmen, four or five ranks deep, sufficing for your front, with two more units of spears, a bit behind and on the flanks of your infantry to defend against cavalry flank attacks. In the center, behind your spears, you should deploy your archers with skirmish mode turned off, along with your siege equipment. Cavalry should be deployed on the wings, but farther back than the spears on the flanks. In battle the main thing to pay attention to is focus firing. You should try to keep your archers in two fire groups, and thus have four units of your archers targeting a single enemy unit until it routs before switching targets, while the other four target a different unit. Killing enemy ranged cavalry is the priority, as once the enemy ranged cavalry is gone, your cavalry can chase down and kill the enemy ranged infantry and siege equipment. Be careful about charging your cavalry out while the enemy still has ranged cavalry because the enemy ranged cavalry will circle behind your cavalry shooting it in the back and inflicting heavy casualties. In general, you shouldn't target down enemy melee infantry until they are the only remaining units since the light melee infantry fielded by eastern factions shouldn't be a threat to your spears in combat and will rout easily.

Engaging Pikes
Pikes are the only heavy infantry that your upgraded and trained heavy infantry may have trouble fighting against. In head to head combat, you will deal very few casualties, although the high melee defence of your heavy infantry means they should take damage relatively slowly. Once the enemy pikemen are engaged on the front, you can bring other heavy infantry around the back and crush the enveloped pikemen. Cavalry charges into the back of pikemen are also devastating, but make sure that your cavalry are done disposing of the enemy ranged troops before committing them against the pikes. If you can avoid fighting the pikemen in melee so much the better. Ballistas make quick work of clustered pikes and archers deal heavy damage, particularly from behind. If you can kill all the non-pike units first, you should be able to evade the pikes while shooting them down. The eastern composition is particularly good for this, but be careful about engaging pikes from the front with thureos spears, as they are substantially lighter than true heavy infantry and will take heavy casualties quickly.

Engaging Elephants
Only rarely will you run into an enemy deploying elephants, but it is imperative to focus fire all available missile troops on the elephants to kill them as quickly as possible because they can inflict terrible casualties even on top tier swordsmen when they charge. If you know you will be fighting elephants, it may be worth while to pick up some peltasts or javelin men as they have a hidden bonus against elephants. Thracian peltasts and Dacian heavy skirmishers are both excellent units against elephants which also have utility against other light troops as they have very good melee stats for a javelin armed unit. Everything said of elephants is also true of chariots, although they do less damage and are in general a lesser threat.

Attacking a City
Army composition is almost irrelevant in siege combat against the AI, but a couple of units of heavy infantry and one unit of siege equipment are important when attacking, and thus the western composition is slightly better. When deploying your units, deploy your ballistas and two units of heavy infantry with two ladders and two units of archers on one side of the settlement, preferrably close to the victory point and on a route with relatively few towers. Then deploy the rest of your army in plain view on the other side of the city. In many cases, the entire enemy garrison will deploy on the walls against most of your army. After your ballistas level any nearby towers, you can send your two units of heavy infantry over the undefended wall, seize the victory point, and win the battle. Sometimes enemy pikemen or other infantry will be deployed in the town square and you should bring up your archers to dispose of them before seizing the square.

Defending a City
Both eastern and western compositions work very well for siege defense. Put heavy infantry on the walls where the enemy siege ladders or towers are aimed and deploy ranged infantry on the wall to the sides. Thureos spears may be worsted in combat by heavy infantry, but the damage dealt by towers and ranged attacks should mean that the enemy heavy infantry is heavily wounded by the time it enters combat, and thus it shouldn't be overly problematic.