A Rite of War was a formalised doctrine of battle, a codified way of waging conflict that a Legion or its commanders might invoke to reshape an entire force toward a singular strategic purpose. To declare a Rite of War was no light matter; it demanded the assent of a Legion's high command and bound its warriors to a particular philosophy of slaughter for the duration of a campaign.
Each Legion nurtured its own Rites, born of the temperament of its primarch and the hard lessons of the Crusade. The Iron Warriors mastered the grinding attrition of siegecraft, while the World Eaters embraced doctrines of headlong butchery that flung armour and blade into the enemy's heart without care for cost.
A Rite reflected the very identity of those who fought beneath it, and to choose one was to declare what kind of warriors the Legion would be. In the fires of the Heresy, these doctrines hardened into weapons of civil war, each Legion turning its perfected art upon brothers who had once fought at its side.