From Warhammer 40k - Lexicanum
The Triarii were a specialized formation of World Eaters during the Great Crusade and Horus Heresy. Consisting of five Companies, the Triarii specialized in ship-to-ship boarding actions.
After the Horus Heresy, some of the Triarii went on to form the Riven and join the Black Legion.
- Delvarus - Centurion
- 1: Betrayer (Novel) Chapter 7
- 2: Black Legion (Novel), Terra