Battle of the Carchera System
As the Horus Heresy neared its end, Roboute Guilliman made all haste for Terra in the hope that they would reach the world before it was invaded by the Warmaster's forces. However the Ultramarines had to pass through the Carchera System to do so and were then forced to fight the Iron Warriors of Warsmith Khrossus, who had seized control of the System. The Iron Warriors had been sent there by Perturabo on the orders of Horus, who hoped to delay the Ultramarine advance. The overstretched and under-equipped Iron Warriors had little prospect of victory, but nonetheless were able to put up substantial resistance in their delaying action against loyalist forces.