The Solar Auxilia were the elite void-soldiers of the Imperial Army, disciplined human regiments hardened by war beyond the light of any sun. Where common Army levies fought across a thousand worlds under a thousand banners, the Auxilia were a corps apart, veterans of the deep-void campaigns whose iron cohesion and heavy war-gear set them among the finest mortal fighters of the age.
Encased in environmentally-sealed void plate and marching in tight, drilled formations, they were trained to hold the line where lesser men would break, standing firm against horrors that shattered the resolve of ordinary soldiers. They fought often beside the Legions themselves, and their armoured columns and battle-tanks lent weight to campaigns too vast for even the Astartes to win alone.
The Solar Auxilia prided themselves on unshakeable discipline and grim professionalism, a martial culture forged in the cold dark. When the Heresy divided the galaxy, these mortal legions were swept up in the slaughter, their loyalty as bitterly contested as that of the transhuman warriors they served alongside.