For "Legion of the Dead," I reviewed past sourcebooks featuring the Hegemony, including (but not limited to):
1) The Periphery (1st edition)
2) The Periphery (2nd edition)
3) A Guide to Covert Ops (where a lot of the terminology for the Ordo Vigilis comes from)
4) Handbook: Major Periphery States
5) Field Manual: Periphery
6) Field Manual: 3145
7) Era Report: 3145

Shattered Fortress
9) Empire Alone
10) Objectives: Periphery