Horus Heresy: Liber Mechanicum

Reviewing the new Mechanicum army book for Warhammer the Horus Heresy!

Today I’m review the new Liber Mechanicus book for Warhammer the Horus Heresy. First, thanks goes to Games Workshop for providing this to review for free. As always I aim to honest, impartial and constructively critical. Now onto the review!

Inside the Liber Mechanicum you’ll find everything you need to field either a Mechanicum army, Titan army or Imperial Knight army for your games in the Age of Darkness. It’s 124 pages of quality content, coming in the new black hardback standard of the Horus Heresy rulebooks. Thankfully, it’s not as heavy as the Legion books but more comparable to a current Warhammer 40,000 codex for weight. You’ll also get a decent volume of narrative content for each 3 factions too, which is nice too.

For the Mechanicum section, I like how the book establishes what core and expanded units are, very helpful. It also covers what you need to do to build a Mechanicum army. Basically you decide whether you’re a traitor or loyalist and then build your army list as normal, making compatibility with the current tournament and game formats easy. Your allegiance matrix remains unchanged too from the core rules.

Their advanced reaction is crazy powerful. It triggers when a unit with an independent character is shot at. That unit and everyone within 12 of that friendly unit shoots the attacker. Incredibly strong but still has some counter play, namely shooting non-independent supporting characters first to minimise it to be a normal return fire reaction. Still incredibly power but yeah.

You get a decent spread of HQ and Troops units, to name a few. The only thing that holds you back is the cost of Forge World resin. Still, you get to field loads of lovely robots, twisting the dynamic on Space Marine vs Space Marine combat as a lot of your units or mini monstrous creatures with +3 to +4 saves.

Next you get Titan armies. Your troops are just minor Secutarii units but the big thing is being able to take titans. Warhounds are 750, Reavers 1,500, Warbringers 2,000 and Warlords are 3,000. These titans can be used in normal army lists following the normal allowances for Lords of War by points limit (so only a Warhound at 3,000 point games). You have another optional allied detachment shown above which cannot be taken as a main detachment. Overall it’s a neat way to include titans, although seemingly no way to include an entire army of titans (which I’m thankful for personally) in normal point games.

Next you have Questoris Knights. You can either take a Knight as an allied slot in a normal army’s Lord of War slot or use their own force organisation chart and ignoring the 25% Lord of War limit for that detachment. For a main army you have to have 2 troops choices to unlock a single Lord of War slot.

Frustratingly, Armigers are pretty great and you may see more of them spammed over actual knights as they’re now monstrous creatures basically like Dreadnoughts. They are around the same price as a Contemptor but lack the +2 save or WS/BS 5, so that’s something at least.However base Reaper Chainblade and Thermal lance is a pretty strong combo.

Knights are still quite pricey but have 7 to 9 hull points, a +5 invun (+4 from the front) and some powerful weapons. Yet being vehicles is probably their biggest weakness, especially with the buff to heavy support squads, infantry and weapons like las cannons. Overall it does look pretty balanced overall, although I expect Armigers to do most of the work and get more commonly seen.

Next you get lots of unique rules such as with ranks for your knights. Nifty narrative and gameplay-boosting upgrades. The book also covers all the shared unique special rules found within as well as listing all the weapon profiles too. I really love the return of universal special rules.

Finally you also get a plethora of unit artwork and display painted miniatures to show off the range of miniatures from everything inside the book. Really great and gives you lots of ideas for painting as well as the scale of these units.

Liber Mechanicum Overview

Overall this book is pretty great, even if I’m not a Mechanicum fan myself (Alpha Legion forever!). If you want to play a Mechanicum army, use Titans or field a Knight army, then this is for you. Things seem mostly balanced too and it’s going to be fun to see the return of Mechanicum robot armies to the table in the new edition of the game.


  • Clearly and well-presented book
  • Balanced, thematic yet strong rules for mostly everything included
  • Compatible for Space Marine players too if players want to slot in these units for their armies


  • Most of the range is currently Forge World only, making armies expensive and locked to resin with almost no pure-plastic kits
  • Knights (Armiger Spam) potentially could be overpowered

You can order your Horus Heresy products directly from Games Workshop or via my affiliate link at Element Games that will net you a 15% to 25% at no additional cost to yourself while helping to support me and my content, so check it out if you can.

Check out my Discord as well as my Patreon too if you want to give me some more support!

That’s pretty much it for now. Once again, another solid release for the Horus Heresy. For myself, I’m going to go back to working on my Alpha Legion army. So until next time you can always roll crits, even when facing off against the Mechanicum and their knightly armies!

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