When the Anargo sector was first colonized, during the Age of Technology, Fornax was among the first worlds to be visited by settlers. Although some scholars have wondered why this world was among the first to be colonized, when it is not amongst the most desirable worlds in the sector in terms of living conditions or mineral wealth, the answer lies in the principle of serendipity. During this time, warp travel was a far more dangerous and unpredictable affair than it would be after the founding of the Astronomican. Each journey into the unknown was as unpredictable as a lottery, and the rewards could be discovering ancient riches and earth-like paradise, or suffering a horrific fate during warp travel. Like many other worlds, Fornax was colonized because it could support a large human colony and its settlers did not dare going further.

Fornax was originally colonized by two different colonization fleets, the Naurati and the Mircan. Although determined to live together in peace, the cultural differences between the Naurati and the Mircan was quickly evident as civilization flourished. In contrast to the conservative and wary Naurati, the Mircan experimented frequently with the nature of the warp. The Mircan were quick to realize that there were certain powers in the warp that could not be trusted and thus avoided corruption by Chaos. Nevertheless, the unnatural quality of the warp influenced the Mircan in body and mind. Even without dealing with the ruinous powers, they changed, and the birth of psykers became increasingly common, while newborn Mircan were visibly different from their parents. Asymmetric bodies and facial features were increasingly common, but the Mircan viewed this as a sign of evolution rather than rejecting their offspring. In the minds of the Mircan, they were the future of mankind, evolving to become a race of psykers that would ultimately rule both the Materium and the Immaterium. The Naurati were so shocked and appalled at this development that they declared war on the mutants.

Because neither side had built up any significant military powers capable of invading by the time the war broke out, and because both sides were roughly equal in terms of economy and natural resources, the war between the Naurati and Mircan became something of a stalemate and dragged out over centuries, millennia. Through the long Age of Strife, the two factions waged war, but neither side was willing to resort to weapons of mass destruction, both in fear of retaliation and fearing the long-term global consequences. When the Imperial forces arrived in the Anargo sector in M30, the war on Fornax had lasted thousands of years and both sides were on the brink of collapse. Transmitting from a grand cruiser in low orbit, Imperial Emissary Viscount Paul Gabriel Khatchetlova demanded that the entire population of Fornax should submit to the Imperium immediately and pledge their allegiance or be destroyed. In a matter of hours, both the Naurati and Mircan sent shuttles racing to the Imperial grand cruiser to plead to the Viscount for aid in the war. While the Mircan waited on the surface, hoping that this unknown galactic power would see their potential, come to their aid and give them their freedom, they received a video transmission which would later become historical. From the airlock of their grand cruiser, Imperial troops ejected the decapitated body of the mutated Mircan negotiator, recording as the body fell towards the planet below, catching fire as it passed through the planet’s atmosphere. Only moments after the transmission ended, the Imperial fleet began its bombardment. A civilization that had existed for seven thousand years and fought for its own survival for the majority of its existence was utterly destroyed in a matter of hours.

When the smoke, dust and fire of the nuclear holocaust finally settled, Imperial forces supported by Naurati troops immediately launched an attack of the radioactive wasteland that had once been the Mircan civilization, slaughtering any military forces or civilians that had miraculously survived the destruction. As history would show, however, the Imperial forces, under command of Alpharius himself, were too eager to declare victory and move on.

Although Fornax was fortunate enough to remain mostly untouched by the wars of Horus Heresy, due primarily to the fact that the world was so ravaged by war that it had little strategic value, the Age of Imperium was by no means an easy time for the people of Fornax. As the sector struggled to rebuild after the Horus Heresy, followed by a vast crusade against alien forces in the sector, there was little support available for the Fornaci. Things were, however, constantly improving compared to the days of war against the mutant Mircan, and with a moderate mineral wealth at their disposal, the Fornaci began the slow process of industrialization.

During the Age of Apostasy, Fornax was one of the greatest allies of the Adeptus Ministorum and the Dorvastor-Anargan alliance. The Fornaci people were second to none in their devotion and provided a tremendous pool of recruits for the growing Frateris Templar. Under the banners of the Adeptus Ministorum, the Fornaci Templars waged war against many Imperial worlds in the Anargo sector that failed to meet the demands of the Administratum and Ministorum. As reward for their loyalty, the Imperial authorities in the Anargo sector invested great resources in Fornax in order to establish the Anargo subsector as the supreme industrial and economical power in the sector. Meanwhile, worlds across the sector paid for these investments in blood.

When the Dorvastor-Anargan alliance fell and the forces of Sebastian Thor liberated the Anargo sector and restored unity, the cultural and societal changes on Fornax were monumental. Virtually overnight, the majority of the Fornaci people rejected the Adeptus Ministorum and many abandoned their faith entirely, forming new churches or even turning to their old religions. Those who remained loyal to the Adeptus Ministorum were all too eager to persecute such heretics and so the majority was divided between Imperial faith and a private faith.

In M39, a series of terrorist attacks made it clear that the old enemy, the mutants formerly known as Mircan, had returned. Somehow, the mutants that had survived nuclear holocaust had lingered, surviving in ancient bunkers and mines, or even infiltrating the slums and sewers of the Naurati. Over the years, the small and isolated mutant communities had united in secret and now formed a considerable threat to Fornax. Even though only a small minority of the mutants were executing the terrorist attacks against the public, the presence of uncontrolled mutant psykers spread across the planet struck fear into the hearts of the Fornaci and Imperial authorities alike. Furthermore, religious groups pointed to the return of the mutants as punishment by the Emperor, arguing that this was due to the increasing secularization on Fornax. For the past centuries, Fornax has seen an increasing polarization between secular groups and the growing religious minority.