The Solar Auxilia are the most elite division of the Imperial Army, mortal soldiers trained to fight in alien atmospheres, toxic death zones, and even the cold vacuum of space – the most hazardous battlefields of the Great Crusade. Equipped with sophisticated wargear and sealed environmental armour, the Auxilia are recruited from across the Imperium's many conquests, chosen for a mix of skill, discipline, and raw aggression. As the Age of Darkness sweeps across the stars, the countless cohorts of the Solar Auxilia must each declare their allegiance – honour their Warmaster, or stand with their Emperor?