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 Legions[]
| № | 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 |