Developer Diary | Combat

PDX Katten

Jul 26, 2023
Hello, everyone. Ian Fischer of C Prompt Games here again, excited to share another Developer Diary for Millennia. We are heads-down working on our end-of-year objectives but I am going to take a quick break from that to talk about combat.

Goals of Combat

Before we get to specifics, let’s outline some of our goals.

To start with, we want Millennia’s combat to be “inline.” There are a lot of strategy games with tactical combat that we love (how ya doin’, Age of Wonders), but Millennia is primarily about the arc of history and our goal is to keep the focus at that level. We want you thinking more about technologies, government types, the growth of cities, and the course of wars, less about “that archer should take cover behind that tree.”

To support this, combat choices in Millennia are at the strategic level -- you decide who fights who, where, and when, but you do not give orders during combat. Similarly, combat is presented in window atop the world map and provides controls that allow you to analyze or quickly resolve a battle as you want. This is intended to show combat while still keeping you in the flow of the game as much as possible.

Secondly, we want combat to be manageable. In the early stages of a 4X, you tend to have a small number of units. These are important, easy to keep track of, and you often have a specific plan for each of them. Contrast this with not-uncommon mid- to late-game conditions, where you have a multitude of units, you spend a chunk of your turn trying to remember what you were thinking when you sent someone with a club to the other side of the planet 20 turns ago, and “plans” sometimes tend more toward masterful stratagems like “send everything here.”

We want to do what we can to keep things trending more in the early game feel. Some of this is accomplished with core game balance and UI support like the Outliner or the ability to name Armies, but the biggest contributor is having combat built around multiple Unit Armies.

One of the two stylistic approaches to naming Armies...

Armies size starts at three but can grow to seven later in the game. Larger numbers of Units are thus grouped into a smaller number of Armies to command, plan around, and keep track of.

Finally, like almost everything, one of our goals is to have interesting choices at the heart of the gameplay. We like making combat inline and not having tactical choices during the fighting – but we want solid strategic choices about the fighting. Armies are a good structure to focus decisions around warfare – but there need to be interesting decisions about how you build Armies for it to be worthwhile.

Our core combat mechanics (which we’ll talk about next) are organized largely around supporting this objective.

Basics of Combat

This will go poorly for you, Roman Raiders.

Battles in Millennia are generally structured around one Army fighting another Army.

The fighting is resolved during up to three rounds of combat. All of the Units in each Army get to take an action during each round. If an attacker wins the fight, their Army moves into the space that was occupied by their target and the defender (assuming any of them are still around) retreats. If there is no winner after all three rounds, the battle is considered a “push” and both Armies remain in their original locations.

During a round of combat, one Unit in an Army will target an enemy Unit. This causes the attacking Unit’s Attack value to be compared to the target’s Defense value. From the result, damage is determined and applied to the target Unit’s Health and Organization.

Health is something of a “normalized” value, meaning that Millennia uses it primarily as a way to scale lethality overall, not as a differentiating factor -- the majority of Units (but not all) have 50 health.

Organization, which is somewhat related to Health, is a differentiating factor and different Units have different Organization values despite having the same Health.

At zero or less Health, a Unit is destroyed. At zero or less Organization, a Unit is routed and attempts to flee the fight. Damage to Health is recovered over several turns (it is faster if the damaged Unit is recovering within its own territory, including territory held by an Outpost). Damage to Organization is fully recovered at the start of the next turn.

Additional factors, such as the terrain where a fight takes place or an Army being fortified, can further modify combat, but this is the basic arrangement.

Unit Types

Unit Types inject interesting gameplay into these core mechanics by adjusting various rules of the combat system.

With all of the Variant Ages, Crisis Ages, National Spirits, and upgrades through the Ages, there are close to 250 Units in Millennia. While many of these have unique characteristics, almost all of them have one of three basic Types and the Type defines their general operation.

Support Type Units are Units like Archers. In Millennia, Units of this type have the ability to do a lot of damage, but they need protection – they are relatively weak in direct combat.

Support Units go first in each round of combat and they select their targets at random. (If you believe in luck, you can run all Support Type Armies and hope your initial attack is enough to cripple the enemy Army.)

Line Type Units are what is supposed to protect the Support Types. Line Type are Units like Spear in the early game, evolving into Pike, then Musket, then Assault Rifle in later Ages. Line Units tend to do less damage but have strong Defense and Organization.

Line Units go second in each round of combat. From a targeting perspective, if there are Line Units that are valid targets, they must be attacked before other Units can be engaged (when there are multiple valid enemy targets, Line Types select one to attack at random). Hence, stacking Line Units in an Army is a good way to keep damage-dealing Supports alive.

Mobile Type Units represent “maneuver warfare.” These are Units, like Knights or (later) Main Battle Tanks, that are intended to make a mess of things by showing up in places where the enemy doesn’t want to see them.

Mobile Types go last in each round of combat. If there are enemy Line Units present, Mobiles must target these first but, representing their ability to strike at enemy weak points, Mobile Types don’t select targets at random, instead always picking the valid target with the lowest Health.

Additionally, Mobile Types do double the normal damage to enemy Organization, representing the cavalry charges or similar shock tactics. With the focused targeting and shock damage, Mobile Type Units are useful for breaking enemy Line defenders and then chasing down any Supports they might be protecting.

Warfare Domain

Combat, as part of a 4X, generally involves considerations beyond just the actual fighting and composition of Armies – economic factors play a part too.

The typical considerations that flow from that structure, like Unit Production and Upkeep Costs, are part of Millennia’s combat system. Similar to the way that the Types rules introduce an additional dimension to how you think about your Armies, the Domains in Millennia create another dimension for the economic interaction with warfare, beyond the “typical” material.

To begin with, not all Units in Millennia are built at the Capitals with Production. There are a number of Domain Powers that can be used to spawn Units or Armies. For example, the starting Tribal Government includes Raise Tribal Army, which allows you to spawn a Warband at a Capital using Government Domain.

It costs some political capital to raise the tribal army, but it’s a good option for defending Towns when surprises happen.

Units that are part of a particular National Spirit often have ways to earn or deploy these Units that are not the standard “build them with Production.” This allows a variety of economic plan and National Spirit combinations that can produce unique approaches to war.

The Warfare Domain itself has a number of National Spirits that are focused on war (as you might imagine), but even the basic Warfare Domain Powers that all Nations have access to influence combat heavily. Warfare Domain Powers like Forced March and Reinforcements can be used get Armies (of whatever composition) where you want them or to heal them after a fight. These uses also compete with upgrading older Units to more modern (and more powerful) versions when you advance in Ages, which has a Warfare Domain cost.

Get with the times!

In general, a reserve of Warfare Domain represents a Nation’s overall preparation for war. If you’re going to be fighting, you want to have some Warfare Domain in the bank to use Domain Powers, upgrade Units, and make the most of your National Spirits.


There are several sources for Leaders in Millennia, but the basic way to get one is to make your own via promotion.

As Units fight in Millennia, they gain experience, which eventually translates into levels of Veterancy. Each level of Veterancy increases the Unit’s Attack and Defense, but Veterancy also allows a Unit to be promoted into a Leader (at a cost of Warfare Domain).

Leaders are reasonably capable Units on their own, but their true value is in the bonus they apply to other Units in their Army.

Leaders have a Tactics value. When combat occurs, the Leaders with the highest Tactics value on each side (you generally do not want more than one Leader in an Army) are compared and the difference between their scores becomes a bonus for the side with higher Tactics leader.

Each level of the Tactics bonus is, essentially, an additional level of Veterancy for ALL Units in the Army, so good Leaders can provide a considerable advantage.

Leaders start with a Tactics value that depends on the corresponding Age of the Unit promoted – an Age 1 Warband will promote into a 1 Tactics Leader while an Age 2 Spear will promote into a 2 Tactics Leader. Gaining levels of Veterancy will further increase a Leader’s Tactics value.

Hence, the total potential Tactics value of a Leader caps out at maximum Veterancy, which means that Units from later Ages promoted into leaders always have a higher maximum Tactics level than Leaders from earlier Ages. Once a Unit has been promoted into a Leader, it can no longer be upgraded, which means it generally becomes outclassed over time.

When Leaders get a little long in the tooth, a Unit ability can be used to Retire the Leader, which provides a Warfare Domain reward.
image4 (1).png

Agamemnon, heretofore not known to have commanded Main Battle Tanks.

(Overall, this means that Leaders can be very powerful for their Age, and the spirit of what they did can live on productively into the next Age or so, but generally you don’t want the Leader you had in the Stone Age to stick around to the end of the game.)


We hope you have enjoyed this look at combat in Millennia. While we covered a lot of the basics, combat is a deep system and there are aspects we didn’t get into or only touched on at a high level. Still, I hope the basic shape of things came across, especially the interplay of all the decisions – your economy, your National Spirits, how you compose your Armies, and how you manage your Warfare Domain all work together and provide a lot of options for crafting fun approaches to fighting.

We’ll be back on 14th of November to talk about Economy part one. As usual, if you like what you have seen, please Wishlist us!
Very interesting, thanks.After seeing the pictures I first thought of a combat system like in AoW or in Civ: Call To Power, but you clarified that. Not sure if this will be better, but I'm curious to see.
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The actual tactical combat seems more "stylized" than I would prefer, but the emphasis on Strategic rather than Tactical decisions is dead on and keeping battles confined to a single tile/hex and turn keeps them far better aligned with the game's Grand Strategy map and time scale.
Will be interesting to see how the exact interactions work in practice, especially when dealing with technologically mis-matched units ("Colonial Warfare").
I have been waiting for this since I was disappointed that Civ 3 did not use Call to powers combat system. I like Old world a lot but their combat system is somehow even worse than the later Civ games one unit per tile. They give units way to much moves that it is almost impossible to keep a front line. I wish this or something similar will be used in all future 4x games.
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