This archive tracks four layers. A record present in 4 of them (HH, AoI, M41, IND) is silent in the rest, and says so.
The Horus HeresyM30–M31
imperium
Pylon world at the mouth of the Eye
Already old and already strange: thousands of black pylons of unknown make stand on its surface, predating any human colony. The Word Bearers came here on their way into the warp.
Age of the ImperiumM32–M40
imperium
Fortress world of the Cadian Gate
Fortified over millennia into the cork in the only reliably stable corridor out of the Eye of Terror.
The 41st Millenniumpre-Rift
imperium
Fortress world; every citizen a soldier
Kasr after kasr, and a population conscripted from childhood. Twelve Black Crusades broke on it. The pylons, nobody realised, were what held the Eye in check.
Era Indomituspost-Rift
chaos
Destroyed; daemon world
Abaddon dropped a Blackstone Fortress onto it in 999.M41. The pylons died with the planet and the Great Rift tore open; the ruin has since passed from the Black Legion to the Iron Warriors.
Position
Map frame: 232, 348 in the archive's 0–1000 disk space (core at 500, 500).
Distance from the core: 308 units ≈ 32.8k light years, north-west of the galactic core.
Height above the disk plane: 0.1 units — invented thin-disk jitter, deterministic per record. No published source gives any location a z coordinate.
System: Cadian System
Books set here
11 titles in the reading tracker touch this record, 7 of them as a primary location. Titles link out to the tracker.
wh40k.lexicanum.com/wiki/Cadian_System derived: — 'lies at the edge of the Eye of Terror, within a narrow corridor of stable space known as the Cadian Gate'. Placed just outside our Eye of Terror feature on the Imperium-facing side, almost due galactic-south of it and due north of Terra, so the Gate reads as the door between the Eye and the Throneworld
classhigh
wh40k.lexicanum.com/wiki/Cadia infobox Class = Dead World / Daemon World / former Fortress World / Martyr World; rendered as a fortress with a destroyed state in indomitus
riftSidelow
derived geometrically: no published source assigns Cadia's ruin to Sanctus or Nihilus; it sits in the Rift's western mouth