From Warhammer 40k - Lexicanum
Astilaeus was a member of the Dark Angels during the Horus Heresy.
Astilaeus was a Cenobite of the Order of the Empty Sky. Deployed during the Thramas Crusade, Astilaeus and the other members of his Order made available their expertise in close-quarters combat in conjunction with artillery support. This specialization of his Order began on Caliban when heavily armored knights would fight even as their serfs and armsmen showered the field with arrows and bullets. The heavy Terminator Armour worn by Astilaeus allowed him to weather the storm of shrapnel and flame produced by the artillery fire with limited risk.
- 1: The Horus Heresy Book Nine - Crusade, pg. 55