Cthonic System

The Cthonic System is the mined-out gang-world star system almost next door to Terra where Horus was found. Cthonia itself supplied the Luna Wolves and later Sons of Horus from its tunnels until Dark Angels destroyed the world after the Heresy and left an empty well in Segmentum Solar.

This was never a civilised capital. It was a resource pit whose gangs made excellent legionaries and whose proximity to Sol made it politically radioactive once those legionaries turned. Later maps keep the pin because the XVI's origin is a hole in the ground near Terra, not a distant feral romance.

The Cthonic System still belongs on a Heresy chart even though the planet is gone. Unofficial fan summaries keep the segmentum-solar parent and spell the system Cthonic while the world stays Cthonia.