Built above the ruins of Kathmandu[1a] in the Palace's northern regions[3a], the Sanctum Imperialis lies deep within the Inner Palace, past the Eternity Gate which is permanently guarded by two Titans of the Legio Ignatum. The central area of the Sanctum is an expanse known as the Hall of Widows. Further into the Imperial Palace lies the Imperial Dungeon. The Dungeon was built deep underground by the Emperor to be the linchpin of his grand ambition. After a long journey below the surface of Terra, one finally comes before the last door (also called the Silver Door) into the Throneroom of the Emperor himself, which is guarded by a pair of Custodes Contemptor-Galatus Dreadnoughts.[1a] Over the door is the inscription Conservus, Restituere, Revivicarem.
Past the last door the Master of Mankind is eternally seated upon Golden Throne and is accompanied by the 300-strong Hetaeron Guard. Behind the Golden Throne is a dormant Webway Gate, long ago part of the Emperor's ultimate ambition but dormant since being sealed 10,000 years ago. In truth, the Throneroom is itself a massive edifice rather than a simple chamber, for within lies the vast machinery that keep the Golden Throne functional. In the years since the Heresy, the machinery has grown more vast and complex as the requirements to maintain the Throne have increased. The mechanisms of the Golden Throne are like roots that spread all the way to the Astronomicon.
The Tech-priests of the Adeptus Mechanicus constantly maintain the Golden Throne, and they are the only ones besides the Adeptus Custodes and Sisters of Silence allowed to walk these halls. Along the walls of the Throneroom are thousands of outlets connected to the Golden Throne which are inserted with coffins holding a psyker. These serve to initiate the thousand daily sacrifices to keep the Golden Throne operational. Few can withstand to be before the Emperor's presence for very long without being overwhelmed. Even Custodes are are known to fall to their knees before the sight of Him.
The Imperial Dungeon was originally the laboratory where Amar Astarte created the Space Marines. However she destroyed her own lab during the Palace Coup in an attempt to erase her work. The Emperor had foreseen this and copied much of her work, apparently using the lab's destruction as an excuse to clear the chamber for the Webway Project.
Other Areas of the Sanctum Imperialis
- Inner Gardens: Former residential area used by the Emperor which contained a variety of Terran flora and fauna.
- Great Observatory: A gigantic dome in the heart of the Palace, it is two thousand meters high, four kilometers wide, and build from solid marble. Three-hundred meter-wide steps lead to the Observatory, which is itched with the portraits of long-forgotten astronomers. At the center of the observatory hung an arcane device known as the Obsidian Speculum which was used to observe distant galaxies. The Speculum alongside much of the Observatory was damaged beyond repair during the Siege of Terra.
- Hall of Leng: Former residence of the Emperor known to be a place of chronological distortion where it is said he measured the angles of space and time. The Hall exists on a pulled thread in the fabric of space-time, described as a scan on the skin of space. Ancient men built a labyrinthine structure here which the Emperor came to expand upon.
- Villas by the Lake: A gargantuan subterranean cavern which holds a large lake, twenty villas are built around a circular plaza. These villas were intended to be the homes of the Primarchs as they were raised by the Emperor, but their scattering prevented them from ever being used.
- Hall of Victories: A private museum of some of mankind's greatest technological accomplishments. It includes shards of the first clay pot made in antiquity, the Mars Rover, a circuit board from the first Warp Drive, and a tube with the "Mendelian Eukaryotic Genesis Formula", which allowed for the first cloned human.
- Areopeia Junction
- The Emperor's residence, known as the Hall of Leng, may be a reference to the infamous Leng Plateau from the H.P. Lovecraft's Cthulhu Mythos, described as a place where realities merge.
- Portraits of astronomers within the Great Observatory include Algaonice, Galileo, Tycho Brahe, Hypatia, Zulema L'Astròloga, and Caroline Herschel. Also included is a scientist named Zarkov, who may be a reference to the fictional Hans Zarkov from the Flash Gordon series.
- 1: Master of Mankind (Novel) - Part II Choir
- 1a: Chapter 14
- 2: Watchers of the Throne: The Emperor's Legion (Novel) - Chapter 5
- 3: The Lost and the Damned (Novel) -
- 4: Warhammer 40,000 5th Edition Rulebook, p. I
- 5: The First Wall (Novel) Chapter 17
- 6: Valdor: Birth of the Imperium (Novel) Chapters 16-18
- 7: Blood Games (Short Story)
- 8: Deliverance Lost (Novel) Chapter 7
- 9: The Fury of Magnus (Novella) Chapters 9-10
- 10: Echoes of Eternity (Novel) - Chapter 10
- 11: Siegeofterra.com (last accessed 15/2/2023)