|Map||Basic Data||Planetary Image|
An ancient world by Imperial standards, Neptune was first colonized by humanity during the Age of Terra. During the Age of Strife, the planet's inhabitants were mutated into hideous inhuman creatures.
During the early Great Crusade, the task of conquering Neptune and its moons as well as scouring its mutant hordes fell to the vicious IXth Legion. In the tunnels of Neptune's Moons, the IXth Legion fought a bloody war that saw 12,000 Battle-Brothers lost. Yet by the time Imperial reinforcements arrive, the Legion still endured and had succeeded in its mission. They had also replenished their numbers by recruiting among many of the dregs of Neptune.
By the Horus Heresy, Neptune's moons contained Human colonists. During the Solar War, Neptune and its habitats were ravaged by various Pirate and traitor Imperial Army vessels unleashed by Perturabo.
- Triton — The moon is being mined for Corvinium by the Imperium. It was once infested with a Genestealer Cult, until it was recently destroyed by the Adeptus Custodes' Dread Host, when Kallisarian Tristraen Desh personally killed the Genestealer Patriarch.
- Laomedia - Moon. During the Horus Heresy Chaos Cultists unleashed toxic gas into its habits.
- Grylor - orbital colony as large as a Hive city.
- 1: Galaxy in Flames (Novel), [Needs Citation], pg. 280
- 2: The Horus Heresy Book One - Betrayal, pg. 18
- 3: Praetorian of Dorn (Novel), Part 4, Chapter 1
- 4: Codex: Adeptus Custodes (8th Edition), pg. 25 — The Dread Host
- 5: The Horus Heresy Book Eight - Malevolence, pg. 114
- 6: The Solar War (Novel), Chapter 15