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Luna is Terra's single moon. It is the base for massive defense structures defending Terra.
Luna was a renowned center of human genetic research during the Dark Age of Technology, becoming home to massive underground genetic laboratories. During the Age of Strife, it was ruled over by brilliant but fanatical Selenar gene-cults who only submitted to the Emperor after the First Pacification of Luna, the first battle of the Great Crusade. The pacification of the Gene-Cults of Luna allowed the Emperor to mass-produce the Legiones Astartes. As the Crusade expanded outwards, Astartes production on Luna diminished and the Selenar cults lost their importance. The moon was instead given to the Sisters of Silence, Departmento Munitorum centers, and Imperialis Armada defenses.[9a]
During the Horus Heresy's Solar War, Luna was the target of a major traitor attack led by Sons of Horus First Captain Abaddon. During the fighting its massive orbital defense ring was the target of a kamikaze attack by the Battle Barge War Oath and Abaddon captured its remaining gene-labs from loyalist forces. The Selenar Cults, resentful against the Imperium, chose to side with Warmaster Horus and share with him their gene-tech.[9b] After the traitor defeat in the Siege of Terra Luna was reclaimed by loyalists in the Great Scouring.
Ten thousand years later Luna again became a battlefield in the final stage of the Terran Crusade. Due to the reborn Roboute Guilliman's efforts to reach Terra via the Webway, Magnus and his Thousand Sons were able to emerge on the moon. In the subsequent battle the Chaos invaders were defeated thanks to the arrival of Imperial reinforcements from Terra that included the Imperial Fists, Custodes, Battlefleet Solar, and Sisters of Silence.
- Somnus Citadel — Headquarters of the Sisters of Silence
- Port Luna — Naval base for Battlefleet Sol. An enormous shipyard capable of accomodating thousands of starships, at the time of the Horus Heresy it was the largest man-made military structure in history.[2a]
- The Circuit — A massive artificial valley filled with military compounds, command centers, factories, and other facilities.[2a]
- The Ring — A belt of defensive platforms that form a continuous ring around the planet. Made from rock excavated from Luna itself, it is bristling with countless Lance, Torpedo, and Macrocannon batteries.[2a]
- 1: Realm of Chaos: Slaves to Darkness (1988), pg. 241
- 2: The Flight of the Eisenstein (Novel), [Needs Citation]
- 2a: Chapter 15
- 3: The Horus Heresy Book One - Betrayal, pgs. 80–81
- 4: Fantasy Flight Games: Preview the Sol System and Affiliations in Relic: Halls of Terra Expansion (last accessed 12 April 2015)
- 5: Fantasy Flight Games: Announcing a New Expansion for Relic: Halls of Terra (last accessed 12 April 2015)
- 6: Praetorian of Dorn (Novel)[Needs Citation]
- 7: Gathering Storm: Rise of the Primarch, Part 3
- 8: Codex: Adeptus Custodes (8th Edition), pg. 29
- 9: The Solar War (Novel)