This archive tracks four layers. A record present in 1 of them (M41) is silent in the rest, and says so.
The Horus HeresyM30–M31
[RECORD LOST]
No record for this location in The Horus Heresy.
Age of the ImperiumM32–M40
[RECORD LOST]
No record for this location in Age of the Imperium.
The 41st Millenniumpre-Rift
imperium
Mining hive world; the Necron awakening
A relatively recently settled mining world on the outer rim of Segmentum Tempestus, two-thirds built over, with at least seven hive cities and its capital at Hieronymous City, seat of Planetary Governor Talmar Hanrik. It tithes adamantium, plasteel and amacyte, a red jewel found nowhere else. Miners beneath the capital uncover a Necron artefact and wake the tomb under the city, and four regiments of the Death Korps of Krieg come to contain it: the setting of Dead Men Walking. What the war leaves of the world is in the book's spoiler.
Era Indomituspost-Rift
[RECORD LOST]
No record for this location in Era Indomitus.
Position
Map frame: 500, 935 in the archive's 0–1000 disk space (core at 500, 500).
Distance from the core: 435 units ≈ 46.3k light years, south of the galactic core.
Height above the disk plane: 5.8 units — invented thin-disk jitter, deterministic per record. No published source gives any location a z coordinate.
System: Hieronymous System
Books set here
1 title in the reading tracker touches this record, 1 of them as a primary location. Titles link out to the tracker.
Every fact in this record, and where it came from. Editorial derivations say so.
identityhigh
wh40k.lexicanum.com/wiki/Hieronymous_Theta (read directly in a browser on 2026-10-02): 'a Mining World, later discovered to be a Tomb World, in Segmentum Tempestus'; 'located on the outer rim of Segmentum Tempestus, with two-thirds of its surface built over and at least seven hive cities', 'a relatively recently settled world'; capital Hieronymous City; the tithe of adamantium, plasteel and amacyte; the Necron artefact in the mines and the four Death Korps of Krieg regiments; every statement cited to Dead Men Walking (Novel), chs 2-25 and the back cover. Corroborated by Talmar_Hanrik (Governor of Hieronymous Theta), Segmentum_Tempestus (notable planets, citing the e-book ch. 2 pg. 17), List_of_Planetary_Governors, List_of_Commissars, Nuclear_Weapon and Exterminatus, all citing the novel. Black Library's description (Lexicanum Dead_Men_Walking_(Novel)) calls it only 'a mining planet'. NAME-COLLISION CHECK: no other index record uses the name; Lexicanum's full-text search for 'Hieronymous' returns this world and three unrelated people (Hieronymous Klojage, Coyle, Diezen).
segmentumhigh
wh40k.lexicanum.com/wiki/Hieronymous_Theta infobox 'Segmentum: Segmentum Tempestus', System 'Hieronymous System', Sector and Subsector blank, citing the novel ch. 2; https://wh40k.lexicanum.com/wiki/Segmentum_Tempestus lists Hieronymous Theta among its notable planets, citing Dead Men Walking (e-book) ch. 2 pg. 17.
classmedium
'hive' for what the world LOOKS like while the novel is set there: two-thirds of its surface built over, at least seven hive cities, the hive city of Hieronymous City with its High Spire, upper levels and Generatorums (Lexicanum Hieronymous_Theta and Talmar_Hanrik; the page is filed in Category Hive Worlds). Its role, a mining world, is a tithe, not a look, and the infobox Class 'Destroyed by Exterminatus' is the novel's ending, kept to the spoiler. The page gives no terrain or colour word beyond the built-over surface.
gposlow
inferred: the segmentum and a relational bearing are published ('the outer rim of Segmentum Tempestus', Lexicanum Hieronymous_Theta, ch. 2); no sector, neighbour or coordinate is. Placed on the outer, southern edge of this dataset's stylised Tempestus polygon at [500, 935], 25 units inside the rim seam (y 960 between x 456 and 540) and 435 units from the core on a 470-unit disk, at least 67 units from every marker (Gryphonne IV 67, Dasht-i-Kevar 71). The x is editorial, not a bearing. Z 5.8 is the zPolicy value (compute-z.mjs hieronymous-theta 500 935).
erasmedium
m41 only: no permitted source dates the war, and the shelf files Dead Men Walking M41 — Pre-Great Rift (it is not on Lexicanum's List_of_Media_set_during_the_Era_Indomitus). Allegiance 'imperium' per the infobox; 'its solar system, along with the surrounding systems, remained under stable Imperial control' (ch. 2). hh, aoi and indomitus carry nothing: no permitted source speaks of the world in them.
systemIdhigh
'hieronymous': Lexicanum Hieronymous_Theta's infobox names the 'Hieronymous System' (ch. 2) and the page speaks of 'its solar system'. systems/hieronymous.json is a one-body TRUNCATED survey, authored because this is the novel's PRIMARY setting.