Legions were the original Space Marine unit before the Horus Heresy civil war. Each Legion consisted of Space Marines of a single Primarch's gene-seed, making a total of 20 Legions differentiated by Roman numerals I to XX. When the Primarchs were united with their respective Legions, they chose iconic names such as Ultramarines, Blood Angels and Raven Guard.

The size of Legions was not set, and there was much variance, but their strength is estimated at around 10,000 Marines, some perhaps reaching 15,000. After the Horus Heresy, the remaining Legions were divided into smaller Chapters limited to approximately 1,000 Marines each.

The original LegionsEdit

Name (original names) Primarch Details
I Dark Angels (The First) Lion El'Jonson Loyalist
II Unknown Unknown Records lost or destroyed
III Emperor's Children Fulgrim Traitor
IV Iron Warriors Perturabo Traitor
V White Scars Jaghatai Khan Loyalist
VI Space Wolves Leman Russ Loyalist
VII Imperial Fists Rogal Dorn Loyalist
VIII Night Lords Konrad Curze Traitor
IX Blood Angels Sanguinius Loyalist
X Iron Hands Ferrus Manus Loyalist
XI Unknown Unknown Records lost or destroyed
XII World Eaters (War Hounds) Angron Traitor
XIII Ultramarines Roboute Guilliman Loyalist
XIV Death Guard (Dusk Raiders) Mortarion Traitor
XV Thousand Sons Magnus the Red Traitor
XVI Black Legion (Sons of Horus, Luna Wolves) Horus Traitor
XVII Word Bearers (Imperial Heralds) Lorgar Traitor
XVIII Salamanders Vulkan Loyalist
XIX Raven Guard Corax Loyalist
XX Alpha Legion Alpharius & Omegon Traitor