The Iron Vanguard began as the Empire's Vanguard Legions, raised to garrison the Rim in case the thing that took the Cradle ever followed humanity to Aurelia. When the Throne recalled them to fight the civil war, they refused. They had been raised to hold the Rim, and they held it.

For a hundred and forty years the Vanguard's line did not break. Then came the Rim Burning, nineteen days against a swarm that did not tire, and on the twentieth day it broke. The Vanguard has never forgiven itself. It fights with maximum armor, maximum shields and slow, heavy guns, advancing like a closing fist, and it has sworn that the next time the Tide comes, it will not take a single step back.