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Forge World

Orbital radius

1.524 AU


38% Terran normal


average -63° C high 27° C low -140° C






Sector Solar


Segmentum Solar

Mars is the greatest Forge World of the Imperium of Man, producing vast numbers of weapons, vehicles and other technology for the Imperial war efforts throughout the galaxy. Mars is also the homeworld and headquarters of the Adeptus Mechanicus and a planet sacred to the faith of the Cult Mechanicus, which is one reason why travel to the Red Planet for Imperial personnel who are not members of the Mechanicus and share its peculiar faith is restricted. Mars is encircled by a massive conglomeration of thousands of drydocks and other starship manufacturing facilities that encircle the Red Planet in a geosynchronous equatorial orbit that is known as the Ring of Iron. It was the shipyards of the Ring of Iron that constructed the vast exploratory and expeditionary fleets of the Great Crusade and even today produce the majority of the Imperial Navy's capital ships. It is possible that Mars is also the world where the ancient and terrible C'tan known as the Void Dragon has chosen to slumber the eons away.


Mars is the twin planet of Terra, and one of many long-inhabited colony worlds located near the Cradle of Humanity. It is the homeworld and primary power centre of the Adeptus Mechanicus, the ancient and byzantine priesthood of the Machine God, and the heart of their galaxy-spanning monopoly on human science and technology. Following the Unification Wars in which the Emperor of Mankind defeated the techno-barbarians of Terra and reunited humanity's homeworld under a single government, he concluded the Treaty of Mars (known as the Treaty of Olympus within the Mechanicus) with the Cult Mechanicus to unify both Terra and Mars under the umbrella of the newborn Imperium of Man in the 30th Millennium. The Mechanicus recognised the Emperor as the Omnissiah incarnate and swore to lend their technology, the mighty war machines of their Titan Legions and all of their production facilities to the purpose of his Great Crusade to reunite all the scattered worlds of Mankind beneath the rule of the Imperium. In return, the Emperor promised the Mechanicus that it could maintain its political autonomy on Mars and all of its other Forge Worlds and that it would remain immune from adherence to the atheistic doctrines of the Imperial Truth. This ensured that the Adepts of the Mechanicus could still maintain their faith in the Machine God. Therefore, Mars is just as important to the Imperium's survival as Terra itself.

Mars is peppered with towering hive cities, and there is very little of the planet's surface which remains untouched by the constructions of the Mechanicus Tech-priests. Mars had a fully terraformed atmosphere and ecosystems very similar to that of ancient Terra during the Dark Age of Technology, but the constant warfare of the Age of Strife destroyed the world's manufactured oxygen-nitrogen atmosphere and restored the Red Planet's surface to its primordial desert state, absent surface water and breathable oxygen. The only inhabitable regions of the planet are now the Adeptus Mechanicus' hive cities.

Mars is ruled over by the Adeptus Mechanicus' Fabricator General, and he possesses almost every known piece of Standard Template Construct (STC) technology or designs currently in Imperial hands. This is ostensibly so he can construct better and more durable vehicles and technology for the Imperium, although it is fairly clear that the Mechanicus is simply hoarding them.

Its also rumoured that the most powerful of the C'tan, the Void Dragon, sleeps somewhere beneath the surface of Mars, in the Noctis Labyrinthus, and its presence may be the reason why Necron starships briefly landed on the Red Planet in 997.M41. Should the Void Dragon awake, the very heart of the Imperium will tremble.

Planetary Data

Mars Tharsis Map

Map of Mars' Tharsis region at the time of the Horus Heresy in the 31st Millennium

  • Mass: 6.42 x 10^23 kg
  • Diameter: 6787 km
  • Mean density: 3940 kg/m^3
  • Escape velocity: 5000 m/sec
  • Avg. distance from Sun: 1.524 AU
  • Rotation period: 1.026 days
  • Revolution period: 686.98 days
  • Obliquity: 25°
  • Orbit inclination degree): 1.85°
  • Orbit eccentricity: .0.093°
  • Max. surface temperature: 310° K
  • Min. surface temperature: 150° K
  • Visual geometric albedo: 0.15
  • Highest point on surface: Olympus Mons
  • Atmospheric components: 95% carbon dioxide, 3% nitrogen, 1.6% argon
  • Surface materials: basaltic rock and altered materials


  • Warhammer 40,000 Rulebook (5th Edition)
  • Codex: Necrons (3rd Edition)
  • Codex Imperialis

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