During the opening days of the Horus Heresy, it was within the Iron Forge of the Fist of Iron that Fulgrim, Primarch of the Emperor's Children Legion, attempted to sway his brother and great friend Ferrus Manus to the Warmaster Horus' cause of rebellion against the Emperor and his Imperium. Fulgrim had sent the bulk of his III Legion and the 28th Expeditionary Fleet on to meet Horus and the 63rd Expeditionary Fleet in the Istvaan System while he and a small force aided the Iron Hands' 52nd Expeditionary Fleet in retaking the world of Callinedes IV from the Orks. Great bonds of friendship and brotherhood had long existed between the III and X Legions, and Fulgrim felt that he could convince Ferrus of the righteousness of Horus' cause. Fulgrim's hope proved disastrously wrong and the meeting