The Noctis Labyrinth, or Noctis Labyrinthus as it is known in High Gothic, is a region of Mars that lies between the Valles Marineris and the Tharsis Uplands. In Low Gothic, the name translates as "Labyrinth of the Night."
This name is well-earned, for this region of the Red Planet is characterised by a system of steep-walled canyons and valleys that give it the aspect of a naturally-formed maze or labyrinth. The valleys and canyons of the Noctis Labyrinthus were formed by faulting and many show the classic features of grabens, with the upland plain surface preserved on the valley floor.
In some places, the valley floors are composed of rough terrain that has been disturbed by rockfalls created by landslides, and there are places where the land appears to have sunk down to create deep crevasses and sinkholes. It is thought that this faulting was triggered by ancient volcanic activity in the Tharsis region from the ancient time before Mankind first settled Mars. The large complex of mines that were tunnelled deep beneath the Noctis Labyrinthus during the Dark Age of Technology was said to be contaminated by deadly radiation and biological and chemical agents during the great wars between the Mechanicum and its opponents for control of the surface of Mars in the early days of the Age of Strife.
This contamination is supposedly lethal to flesh and mechanical components alike. This claim is not true and is a fabrication created by the ruling Magi of the Mechanicus to keep curious Tech-priests from venturing within the tunnels and disturbing the Dragon of Mars.
The Noctis Labyrinthus is an essentially unpopulated region of the Red Planet as all of the Tech-adepts of the Adeptus Mechanicus who sought to found forge cities there suffered from severe technical problems that ultimately led them to abandon their attempts at settlement.
Deep beneath the Noctis Labyrinthus sleeps the fearful entity known only as the Dragon of Mars in Mechanicus legend. This being may be the C'tan known as Mag'ladroth the Void Dragon, who was supposedly imprisoned there by the Emperor millennia prior during the Age of Terra and is watched over by a single so-called "Guardian of the Dragon" and her companion, a Terran girl named Dalia Cythera and an ancient Mechanicum Protector named Ro-Mu 31, who together have kept watch over the Dragon since the Schism of Mars as the chosen of the Emperor, granted unnaturally long lifespans by His will.
- Codex: Necrons (3rd Edition), pg. 49
- Mechanicum (Novel) by Graham McNeill