Horus Heresy Siege of Cthonia Supplement Review

This week sees the Horus Heresy expansion book Siege of Cthonia going up for pre-order. Siege of Cthonia is the first Horus Heresy expansion book, with 234 pages chock full of lore and new rules. Returning Horus Heresy fans will be familiar with the former Forgeworld “black books” which were often highly limited, coveted, rules books that gave army updates, narrative missions/rules, and an incredible amount of lore; and cost £70-80 on release. This is the new version of those, basically, and instead of being bound in faux leather with silver edged pages with limited print runs that sell out on pre-order it’s in the same binding and look as the 2nd edition army books and rulebook. That’s a good thing. These should be cheaper and more accessible. But is it worth picking up? Games Workshop has sent us a preview copy, which we’re diving into to figure that out.

What’s inside:

  • New Lore
  • New Missions
  • Zone Mortalis Rules
  • Extra rules for Sons of Horus and Imperial Fists
  • Inductii units for every Legion

New Lore

Imperial Fists Castellan Consul. Credit: Jack Hunter

For a book with all of 250 pages, a solid half of it is story – the history of the knock-down-drag-out Siege of Cthonia, the depths of depravity and hatred both traitor and loyalist are driven to, the changing nature of the legions during the heresy and a succession of colour plates illustrating particular warriors.

It’s a high-quality, well written section of narrative, on par with the Heresy 1.0 Black Books, and I think this bodes well for further expansion books for 2.0. The exploration of the Years of Darkness and Blood we get before diving into the Siege is a forest of dangling plot hooks asking you – and Tournament and Event Organisers everywhere – to pick them up and gives you ideas for every combatant force in the game, and the Siege itself is a gripping quasi-historical narrative, carrying on the spirit of the Black Books and their cargo-culting of Osprey publications. We follow an escalating hell-war drawing in more and more legionnaires and allies as war spills out over and under Cthonia.It’s not just Sons of Horus and Imperial Fists – Word Bearers, Alpha Legion, Mechanicum, Militia, Loyalist Thousand Sons and the Shattered Legions (and others – spoilers there though!) all feature as well. It’s full on military history nerd narrative, well illustrated with maps and diagrams and focusing in on tactics and strategy. If you liked the Black Books – or have a long enough memory to remember the Badab War books, which remind me much more of this narrative – you’ll like what you get here and if you’re deep into the narrative of the Horus Heresy, it earns it’s price on this alone.

It’s not a perfect companion to the Black Books though, mainly due to the illustrations and colour plates. They’re good, but few and far between – and not many variant schemes or particularly interesting examples, which would have been nice to see. Better, more frequent “uniform” plates would have nailed this into the high strata of Forge World sourcebooks. Overall the lore section is worth reading if you like this kind of erstatz historical material – very different from the Black Library or the 40k style of narrative and all the better for it.

The Big question for me though is that they put a lot of effort bringing different forces into the narrative – but the book really only presents rules for Sons of Horus and Fists, which is a massive shame and contrary to the narrative presented. With so many different legions and forces playing key roles in the story – in places much more interesting roles than the Sons or Firsts – where are their rules?

Zone Mortalis 

Blood Angel tactical marines seen through a Zone Mortalis door. Credit: Jack Hunter

Instead of wide open battlefields with room for tanks and Titans to rampage freely and cause destruction, some battles during the Age of Darkness are fought aboard spacecraft or in cramped city spaces where specialised infantry get to shine. 

Second edition Heresy was given an initial set of Zone Mortalis (or ZM as it’s often referred) rules with White Dwarf 477 (which is in the Warhammer Vault if you subscribe, something I’ve just used for the first time myself to help write this) and they’ve been updated here. While the rules only took up 7 pages in White Dwarf, they take up about 30 here.

Players are recommended to play 1500-2500 point games using a new, more flexible Force Organization chart that allows for:

  • 1-2 HQ
  • 1-6 Troops
  • 0-4 Elites
  • 0-2 Fast Attack 
  • 0-2 Heavy Support 
  • 0-1 Primarch

While it may seem like you want to load up on HQ and Elite units, there’s a secondary objective in all the missions that gives up 1VP for every HQ or Elite unit killed. If you max out those slots, you potentially give up 6VP, which is somewhere around a third the VP you’ll score from primary objectives in most missions.

Terrain rules have been updated and expanded from what was in White Dwarf, including some strangely written recommendations for using the ZM floor tile set. I think the writers were thinking of the older card tiles from Necromunda with preset layouts on them (or the awful old FW resin tiles), but there are a few guidelines for how you can build your own tiles. The rules for the terrain features and how to set up a board are, of course, separated by seven pages, as they’re clearly not something you’d want to reference at the same time.

You’ve got the same three reactions available as in the White Dwarf rules, though subtly reworded. The Brace reaction, for example, no longer risks you falling back off the table edge.

The biggest change compared to White Dwarf is how you deploy models at the start of the game and coming on from reinforcements as the game progresses. Each Force Organization slot costs a different number of reinforcement points, which are a limited resource that you generate at the start of the game and as each turn progresses. They’re then spent to deploy models, and if you want to deploy reinforcements either on flanking table edges or in your opponent’s deployment zone they cost an additional amount.

There are three core ZM missions designed to be played on a 4×4 board, and then two “apex” missions, which are more narratively inspired and designed around the Cthonia campaign. While one of them works for any loyalist vs traitor game, the other is designed specifically to be played with Thousand Sons vs Word Bearers and is going to be awkward to play with any legions that don’t have substantial numbers of Psyker units.

Tucked away at the very end are a couple additional terrain features that are supposedly themed for the Cthonian underworld, though to me they seem generic enough that they should just be in the core terrain section.

These rules are definitely a step up over the White Dwarf rules and should make for some interesting games, especially as ZM has always been where Horus Heresy is at its best.

New Core Missions 

Imperial Fists move through snowy forests at Goonhammer Open Horus Heresy 2022

Designed for competitive or casual play, there are five new core missions and three different deployment maps to play them on. The only deployments available are Hammer and Anvil, Dawn of War, and Search and Destroy – and the die roll to select them isn’t completely balanced. Half the time you’ll be playing Dawn of War, and only one in six times will you be on Search and Destroy, this lines up with what seems to be gamers general preferences. These missions are designed specifically to be played at 3,000 points. There’s a sentence that I think says you can play with other points totals if you and your opponent both agree to it, but the grammar on that sentence is atrocious so it could also say that the moon is made of cheese, I can’t tell.

All these missions are only four turns long, with no random game length at the end, and use progressive scoring. They also have a uniform set of secondary objectives – Slay the Warlord will be familiar to everyone, but the others, despite sharing some names, have been adjusted from the core rules. There are two secondaries that give you points for killing something in the first turn – First Strike is any time in the first game turn, and Break their Ranks is in your first player turn. I’m not sure why these both exist – the only time I could see it mattering is if the player going second kills something in their opponents first turn (either from a reaction or in an assault) and nothing in their player turn, while the player going first will score both secondaries as soon as they get a single kill.

These missions are all progressive scoring based on objective control, so bringing Line units is key to scoring and winning. There’s no tabling your opponent for a guaranteed win – while that ends the game immediately, victory is still determined by victory points.

While I don’t think I’d call these missions good, they’re at least better than the ones in the core rulebook.

Apex Missions

@itstimins ‘s White Scars holding the line against @fortyk.w ‘s Thousand Sons at No Retreat. Photo Credit – Soggy

Apex missions are a pair of extra fancy campaign missions like we used to see in the black books. Designed specifically for narrative play, these don’t even pretend to be balanced, and recommend that you tailor your list specifically to the mission (require it, really, as one of the two has asymmetrical army sizes).

Both missions have substantial special rules, and look like they’d be interesting to play, though I wouldn’t make them part of a regular rotation.

New Legion Rules

The Cthonia campaign is centered around a fight between the Imperial Fists and Sons of Horus, so both legions have picked up some new wargear, warlord traits, and a named character. While neither of these legions needed more stuff, it makes sense that the stars of the Age of Darkness box would get the first highlights. Hopefully future books are an opportunity to expand on some of the legions with less support.

Imperial Fists

A brave defence by the Imperial Fists against the traitors, Goonhammer Open Horus Heresy 2022

Ferromag Shotguns

A free swap for a standard Astartes shotgun, the Ferromag Shotgun trades 2″ of range, one shot, and Concussive out for Strength 5, AP4, and Breaching (6+). While this can’t be used to reduce WS before a charge, it does give you a cheap infantry weapon that has a chance of cracking terminator armor. Like regular shotguns, these are ‘Auto’ weapons and will benefit from the Fist’s +1 to hit bonus.

Warlord Traits

There are two new warlord traits, Unforgiven and Bound for Glory. Unforgiven is a loyalist-only trait that unusually does not grant any additional reactions. It does make your warlord somewhat more resilient in combat by turning Instant Death attacks from enemy warlords, primarchs, dreadnoughts, knights, and titans into hits that do d3 damage. While you also gain Fearless in combat, you’re forced to declare charges at the closest unit within 12″, which could open you up to a lot of overwatch. While turning off Instant Death seems fairly powerful, you still only have 4 wounds and a dreadnought fist is still Brutal 3, so you’re probably eating shit anyways.

The second trait, Bound for Glory, lets you select a Legion that your warlord will be gaining a bonus against. The timing on this selection is precisely defined as after army selection but before deployment, so even in most events where you have a locked in list you’ll be able to select the legion you’re playing against. It doesn’t, however, let you select anything other than a legion, so you get nothing if you’re playing against Custodes, Sisters of Silence, Mechanicum, Militia, Solar Auxilia, or knights. When locked in combat against the legion you selected the warlord and their unit gets Fearless, but you’re limited to not being able to sweeping advance against that legion. While it does give you an additional reaction in the Assault phase, you should really only even think about this trait if your warlord is in Cataphractii armor already, and even then you should just take Solar Marshal and win the combat instead of worrying about being fearless.

Lord-Castellan Evander Garrius

The new named character has a massive fist (very appropriate) and underslung fancy volkite charger (it’s even got it’s own name – Incineratus). He’s the 456th captain of the Imperial Fists and also known as “The Butcher of Larissan” and “The Tyrant of Cthonia”. Lots of titles. Very impressive. 

With a statline that starts as a Praetor in Terminator Armor, he’s T5, has a 2+ armor save, 4+ invulnerable save, a 5+ Feel No Pain against wounds in the Fight sub-phase, and can still sweep enemy units. His massive power fist is effectively an AP 1 thunder hammer with Reaping Blow (1). Incineratus spits out 5 shots with Deflagrate and Rad Phage, so works either for clearing chaff or trying to knock some toughness off a beefy unit.

Garrius comes with a unique warlord trait that’s clearly tied to the new missions in this book, as the main effect only activates when your opponent has more victory points than you. When they do, however, you get Rage (2) for Garrius and any unit he’s joined. A secondary effect of the warlord trait is you have a chance to reduce victory points your opponent scores from killing units, reducing by 1 on a 6+ normally, or on a 5+ if you’re currently behind on VP. While cool, this runs a bit counter to the first part of the trait, as it makes it a bit harder for your opponent to get ahead on VP. What it can do is help you catch up if you’ve fallen behind, though it’s not reliable enough to count on.

What’s interesting (read: strange) is that he can’t be taken in a detachment when Dorn is in the same detachment, but gains Fearless and It Will Not Die if he’s in the same combat as a friendly Dorn. As you can’t have two detachments of Imperial Fists in the same army, the only time this would come up is if you’re playing with multiple armies and there happens to be another friendly Fist player that happens to bring Dorn and then both of these guys end up in the same combat together. That’s absurdly unlikely to happen unless you specifically set it up to. I understand that this is narrative but believe that you can make narrative rules that will also actually come up in game. 

Sons of Horus

Loyalist Sons of Horus flee from the Emperor’s Children at Goonhammer Open Horus Heresy 2022

Similarly as above, the Sons of Horus also gain new equipment, two new warlord traits, and a new character to lead them in battle. 

Carsoran Power Weapons

The Sons of Horus can swap any Power Weapon out for a Carsoran Power Axe or Power Tabar for no extra cost. The axe is a specialist weapon, making it great to pair with a thunder hammer on a character, and is strength: user with AP3 and Breaching (5+). This makes it a great at-initiative way to chew through power armor. The tabar is strength: +1 (generally making it s5) with breaching (4+). While it’s two handed instead of a specialist weapon, a squad of these that become AP2 on rolls of 4+ is a terrifying image.

Warlord Traits

True Son is traitor-aligned and can’t be used if your primary detachment also has any Daemon or Corrupted units. The Warlord gains +1LD for morale and pinning checks (so not a way to get easier psychic checks) as do any of your units that can see your Warlord; with a note reminding that units that are in combat but not the same combat as the Warlord can’t draw line of sight to them. The warlord also gains re-rolls on armour and invulnerable saves against psychic attacks. While that won’t come up particularly often, it’ll be nice to have when it does. The LD improvement is massive though and worth taking just for that! 

The other, Cast in Gold isn’t tied to traitor or loyalist allegiance. It’s designed around having your warlord challenge enemies of equal or higher weapon skill (most likely equal, given that your warlord is likely a praetor). When you are in a challenge against such an opponent, you’ll pick up +1 strength and +1 attack, and assuming you slay the opponent you get +1 additional victory point.

Vheren Ashurhaddon

The Cadre-captain of the Sons of Horus, the First Reaver, and the Master of the True Sons. Not quite as many titles as our yellow friend above, but impressive nonetheless. Instead of being a durable brick in terminator armor, Vheren is Weapon Skill 7 and Strength 5 with Precision Shots/Strikes (6+) and Counter Attack, making him good at rolling into a squad and killing anything important – especially given his at-initiative AP2 axe.

Vheren’s armor also gives him a bit of extra durability – against shooting attacks Vheren (and his unit) count as being 3″ further away from enemies. It does take a bit of precision to make effective use of, but you can use this to avoid getting hit by rapid fire or melta while still being able to get your own attacks in.

His Warlord trait is odd: when you (the player using Vheren) allocate wounds to him you get to re-roll any failed invulnerable saves. Not if the wounds were allocated by your opponent such as by snipers, but if you yourself are choosing to make the save on him. Between his 4+ invulnerable save and Battle Hardened (1) you could tank lascannon shots on him if you really want to, but often you won’t want to even possibly suffer a wound on him. 

As the First Reaver he’s able to take a Reaver Attack Squad as a retinue where he becomes the unit’s leader. This unit gains the Line subtype making them solid for objective play, but you’re going to need a transport to get them there if you’re not playing Zone Mortalis! 

Legion Decurions

Kratos Heavy Assault Tank. Credit: Rockfish
Kratos Heavy Assault Tank. Credit: Rockfish

Decurions are upgrades that you can buy for some Predators, Sicarans, Sicaran Punishers and Kratos. Everyone can have the generic Defensor or Locus. The Lanius joins the Sons of Horus and the Imperial Fists get the Sagittar. You have to buy a pintle weapon at extra cost for the generic guys but the Legion-specific ones come with pre-set guns.

The rules do specifically state that you have to visually represent the Decurion with a model sticking out of a hatch on the tank, but I can’t imagine that this is actually going be enforced anywhere outside of Nottingham, as long as it’s clear.

We’ve got a detailed Tactica upcoming on the Decurions, but in short:

  • The Defensor (and his squadron) get to return fire or overwatch with their pintle weapons firing twice.
  • The Locus gets to return fire (but not overwatch) with one battle weapon – which is a big deal.
  • The Lanius enforces discipline among the Sons of Horus by waving a flag about and shooting them with his Banestrike Bolt Cannon if they run away.
  • The Sagittar can fire his assault cannon, or another defensive weapon, with skyfire or precision shots. Sniper Sicaran Punisher, anyone?

We like these. They add a bit more character and power to vehicles, which they need. Whether the price of them is worthwhile will probably depend on the size of the tank you’re sticking them in. They look great for Kratos and perhaps for squadrons of smaller things. The Locus will be a significant change, letting vehicles return fire with big scary guns – just like everyone else can.

Infernus Abomination

Here we have the rules for the (extremely) Traitor daemon/assassin thing. It’s been a while since this was previewed, but now we have the full rules, and they’re sort of what you’d expect: a chaotic version of the Imperial assassins with extra daemon weirdness.

The Abomination costs about the same as Imperial Assassins and has a similar profile and a similar advanced reaction that lets it move if targeted. But where the Imperial assassins were a bit of a disappointment, these things are quite scary – so much so they actually have Fear (2). It can also regenerate a bit, though it’ll probably be killed outright or not, so that’s not too useful.

The key difference is the armaments it comes with. It’s got a gun called a Boneshard Spitter that is fine, but with only a short range you’ll probably avoid using it, to avoid return fire reactions. You have three choices of attack profile for your Transmutative Armaments in melee and you’ll always choose Hammerblade, because it’s a thunder hammer that strikes at Initiative 5, so you don’t need to know what the other options do. The Spinelash gives you some extra initiative just in case you’re fighting things that don’t have power armor and also have high initiative and also are likely to kill you (you won’t be fighting this), and the Talon-Rakes give you a couple extra attacks and some re-rolls, but that’s strictly worse than being S8 AP2 against pretty much anything, so who gives a shit.

We’ll see Abominations used. Fear is useful, it’s hard to kill due to its reaction and the hammer is a versatile, effective melee weapon. They look to be priced about correctly and give a nice new option for Traitors.


White Scars Despoilers. Credit – Soggy

Over the course of the Heresy the Legions suffered enormous casualties, so they used slightly questionable methods to replace them in a hurry. Inductii are the result and, perhaps surprisingly under the circumstances, they’re great.

The way they work is that you apply a template to an existing unit, rather than create a new datasheet. This template can modify the unit composition and characteristics, while adding or removing unit sub-types, wargear and special rules. Most of these do tend to be unchanged, but each legion does change a few of them.

Downsides of Inductii are that they can’t be joined by any other models, can’t have artificer armour and they are support squads, so they can’t fill your compulsory troop slots. They do remain Line units and keep rules like Fury, Spite and Heart of the Legion unless specifically removed (and often replaced with other, more thematic rules). Generally Heart of the Legion will be the rule replaced.

There’s a template for each Legion so we aren’t going to cover all 18 here. Some get to apply it to tactical marines and others to despoilers. There aren’t any other units that can be Inductii, at least so far, and we’ll be covering these in depth at a later date. 

They can be pretty interesting. For example Dark Angels get to make Inductii Tactical Squads. They lose their Hexagrammaton rule but swap all their Bolters for Volkite Chargers, for free. World Eater Despoilers lose Heart of the Legion and become Ravening Madmen. Alpha Legion tacticals cannot be selected as a shooting target during the first game turn and so on. 

So it’s a variety of things, all quite characterful but probably not game-breaking. A good addition to the game, in general. It’ll be important to clearly mark Inductii squads so your opponent can see who is who.

Final Thoughts

Overall, this is a pretty decent pick up, especially if you’re playing Imperial Fists or Sons of Horus. Players of every legion will benefit from the Decurion and Inductii units and new game options between the new core missions and zone mortalis, while Imperial Fist and Sons of Horus also get some new wargear, characters, and the bulk of the fluff. The missions themselves are ehhhhhhh. I’d rather play with the Goonhammer Approved: Horus Heresy Mission Pack 2023 than these missions, but they’re definitely better than what’s in the core book.