Summary
Games Workshop army-book supplement for the Horus Heresy, codifying the Taghmata Omnissiah and the wider Mechanicum war-host for tabletop play.
Lore
Liber Mechanicum is the army-book supplement published by Games Workshop for Warhammer: The Horus Heresy, dedicated to the forces of the Mechanicum — the Adeptus Mechanicus of M31, before the Schism. The first edition (subtitled Forces of the Omnissiah) was released in 2022 alongside the Age of Darkness 2nd Edition rulebook, parallel to the Liber Astartes and Liber Hereticus but laser-focused on the Priesthood of Mars.
Its subject is the Taghmata Omnissiah — the war-host raised by the Magi for the Great Crusade and the Horus Heresy, encompassing Tech-thralls, Secutarii, Battle-automata of the Legio Cybernetica, superheavy Ordinatus engines, and the assembled cohorts of cyborg infantry. The book frames the Mechanicum as fighting on both sides of the Heresy, easy to ally with any Legio Astartes as Sworn Brothers or Fellow Warriors.
The 3rd Edition (2025) restructures the line: the Mechanicum proper remains in Liber Mechanicum, while the Knight Households and Titan Legions migrate to a separate Liber Questoris. See Knight Household and Collegia Titanica (Adeptus Titanicus).
Contents
The 2nd Edition supplement bundled three army lists — Mechanicum Taghmata, Questoris Households, and Titan Legions. The 3rd Edition splits these and concentrates on the Mechanicum core.
Mechanical categories include:
- High Techno-Arcana sub-factions: Archimandrite, Cybernetica, Lacrymaerta, Myrmidax, Reductor, Malagra, Macrotek — each granting Detachment access and themed rules.
- Cybertheurgic Rites — non-psychic intelligence-based powers (buffs, debuffs) reflecting Mechanicum esoterica.
- Apex and Auxiliary Detachments including the Taghmata Cohort and Apprentice Cadre.
- Machina Malefica — unit profiles for warp-tainted creations, the precursors of the Dark Mechanicum.
Background material covers Mechanicum organisation, heraldry, colour schemes, and lore on the Priesthood of Mars in the Age of Darkness.
Editions and bibliography
- 1st publication (2022) — Liber Mechanicum: Forces of the Omnissiah Army Book, supplement to The Horus Heresy: Age of Darkness 2nd Edition.
- 3rd Edition (2025) — Liber Mechanicum: Forces of the Taghmata Army Book, hardback, 152 pages, released 26 July 2025; companion Liber Questoris carries Knights and Titans.
FAQ and errata are published as PDFs on the Warhammer Community asset host. The book stands beside the in-universe history of the Heresy of Kelbor-Hal as the principal tabletop expression of Mechanicum forces in the Age of Darkness.