Cthonia

Cthonia was the Birthworld on which Horus was raised after crash landing there after being stolen from the grip of the Emperor by the Ruinous Powers. It was also once the Homeworld of the Luna Wolves Legion.

Birthplace of the Great Betrayer
The world of Cthonia 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 Adepts of Mars. The planet that remained was largely redundant and abandoned, completely riddled with catacombs, crumbling industrial plants and exhausted mine-workings.

Fierce gangs inhabited the lawless depths of Cthonia, enjoying freedom from the rigours of Imperial citizenship; but at the time of the First Founding they provided an easy source of Human specimens whom nobody would miss. One report talks of so-called 'recruitment squads' rounding up thousands of gangers and shipping them away, chained together in the holds of prison-shuttles, to geno-laboratories on Luna. Here they were modified using the genetic code of the Primarch Horus. It is more common for Space Marine genetic stock to be gleaned from feral or primitive worlds, however after the usual hypno-psychological indoctrination process, the Luna Wolves recruits emerged as excellent and ferociously loyal specimens.

The Emperor & The Warmaster
Information about Horus himself is even harder to uncover. It is thought that he was the first of the Primarchs to be recovered by the Emperor, having been cast much closer to Terra than the others, and was found at a much younger age. As a result, Horus was for many years the Emperor's only son, and there was a great affinity between them. The Emperor spent much time with his protege, teaching and encouraging him. Horus was soon placed in command of the XVI Legion, renamed the Luna Wolves - ten thousand Space Marines created from his own genetic code. With these warriors to lead, Horus accompanied the Emperor for the first thirty years of the Great Crusade, and together they forged the initial expansion of the young Imperium.

The Horus Heresy
Eventually, a great schism known as the Horus Heresy occurred. This was the first and most devastating civil war in Imperial history. Occurring in M.31 and lasting less than a decade, it divided and nearly destroyed the fledgling Imperium. It marked the end of the Great Crusade and the death of Horus and the ascension of the Emperor of Makind into the Golden Throne.

Cthonia's Fate
The Legion's home world of Cthonia no longer exists, having apparently lost geo-structural integrity and broken apart into asteroids and debris during the centuries following the Heresy. Certainly the once ore-rich planet was riddled with mine workings right through to its dead core (in fact the numerous gangers that formed the population may originally have been imported as work teams to maintain the crumbling tunnels), however there is much conjecture that Cthonia was destroyed deliberately.

Since the destruction of their fortress in the Eye of Terror, the Black Legion is no longer based on any particular planet, instead stationed permanently on various spacecraft. They possess a single ancient battle barge from their original fleet, as well as other vessels commandeered or captured over the years. In particular, many Imperial Navy ships that rebelled during the Horus Heresy now seem to be under Abaddon's command, along with newer vessels he has ordered constructed.