From Lexicanum

This article needs work on its citations. For help on citation see the citation guidelines. You can help Lexicanum by fixing it.

Map	Basic Data		Planetary Image
	Name:	Cthonia
	Segmentum:	Segmentum Solar
	Sector:	Unknown
	Subsector:	Unknown
	System:	Cthonia system
	Population:	Unknown
	Affiliation:	Unknown
	Class:	Destroyed
	Tithe Grade:	N/A

Cthonia was the world on which Horus landed after being stolen from the grip of the Emperor. Also, the Space Marines of the Luna Wolves legion were created using the human stock from various violent hive gangs inhabiting the planets Hives.¹

This planet allegedly existed in one of Earth's closest neighbouring systems. Being within reach even for non-warp spacecraft, Cthonia had been colonised, built upon, tunnelled and mined probably since the dawn of space travel. As such, all natural resources had been stripped away and used up millennia before, and the ancient mining technology had long since been rediscovered and removed by the Adeptus Mechanicus of Mars. The planet that remained was largely redundant and abandoned, completely riddled with catacombs, crumbling industrial plants and exhausted mine-workings.¹

It is listed as destroyed in 3rd edition's Space Marines codex.

Sources

• ¹:Index Astartes IV