Age of the Imperium
From Lexicanum
The Age of the Imperium is the time which followed the Great Scouring and continues to the current time. It was founded on the Codex Astartes, a tome written by Roboute Guilliman. One of the more resisted aspects was the reorganisation of the Space Marine Legions into chapters. This was done to ensure no one ever controlled such a mighty force of warriors again.1
The Codex Astartes became a sacred text as well as the cornerstone on which the Imperium was based. Not only did it reorganise the Space Marines but other decrees rebuilt the Imperium to support its continued existence. Some of the remaining Primarchs resisted the implementation of the Codex Astartes, however all eventually agreed to follow it in the name of solidarity. Since then the Space Marines have followed this pattern and remain resolutely supportive of the Imperium.1
