The Auretian Technocracy was a technologically-advanced and peaceful independent human civilisation scattered across several star systems of the Milky Way Galaxy but centred on their capital world of Aureus. The Technocracy had been founded during the isolation of the Age of Strife and reached its height in the early 31st Millennium. Its technology was of a level equivalent to that of the Imperium of Man at the time of the Great Crusade and in some respects was even more advanced as the Auretians had access to several Standard Template Construct (STC) databases that were not in Imperial hands. The Auretian Technocracy was conquered by the Sons of Horus Space Marine Legion on the orders of the Warmaster Horus in the final days of the Great Crusade. Horus was already planning to unleash his great rebellion against the Emperor of Mankind by the time his Expeditionary Fleet made first contact with the Auretians. The Warmaster used the new technologies and STC databases recovered from the Imperium's brutal conquest of the Technocracy to bribe a faction of the Adeptus Mechanicus into providing crucial logistical and military support to the Traitor forces during the Horus Heresy.
The 63rd Expeditionary Fleet of the Great Crusade, under the direct control of Warmaster Horus and the Sons of Horus, made first contact with the Auretian Technocracy under false pretenses. By this time late in the Great Crusade, Horus had been healed of the terrible wound he had suffered on the moon of Davin after making his deal with the Chaos Gods to overthrow the Emperor of Mankind. As part of the prepartions required to the massive interstellar civil war he was prepared to wage, Horus needed to gain the backing of the Adeptus Mechanicus, as without the logistical, military and materiel aid that the Mechanicus could provide, no war against the Imperium's Loyalists could be won.
After first contact was made with the Auretians by both the Sons of Horus' 63rd Expeditionary Fleet and the World Eaters Legion's 203rd Expeditionary Fleet, Horus invited the Technocracy's leader, the Fabricator Consul Emory Salignac, aboard his flagship, the Battle Barge Vengeful Spirit, under the guise of opening peaceful diplomatic relations between the Imperium and the Technocracy. The Fabricator Consul, who made use of augmetic enhancements much like a Mechanicus Tech-adept, was accompanied by the Auretians' elite warriors, who were known as The Brotherhood and were dressed in Power Armour and made use of Bolter weapons very similar to that of the Space Marines, though they were clearly not genetically enhanced humans and carried no magazines in their bolters. As soon as the Fabricator Consul arrived aboard his vessel, in the course of his welcoming remarks Horus asked the Auretian leader if his people had developed their advanced technology that was so much like the Imperium's own knowledge gleaned from STC databases. When the Fabricator Consul answered in the affirmative, Horus had immediately turned his Bolt Pistol upon Salignac and blew out the back of his head. The Sons of Horus then slaughtered The Brotherhood warriors who had accompanied their leader. Horus justified his actions by claiming that the Fabricator Consul's staff contained a weapon with which the Auretians planned to assassinate Horus to prevent the Imperium from conquering their world. This was an outright lie concocted by Horus to justify the Imperial conquest of Aureus and the acquisition of its STC technologies.
This action initiated a 10 month-long-war between the Imperium and the Auretian Technocracy that would ultimately draw in the Sons of Horus, World Eaters and Emperor's Children Legions. The Astartes Legions laid siege to Aureus and after months of slaughter, the last bastion of Auretian resistance, known as the Iron Citadel, finally fell to the Imperial forces after a two-pronged assault led by the Sons of Horus and the World Eaters, who were led on the field by their Primarch Angron. During the course of this conflict, Horus began the process of turning his Legion against the Emperor, identifying those Loyalists who would not turn against the Imperium to follow him into rebellion and forging links amongst the other Primarchs who were willing to join him in turning Traitor.
After the fall of the Iron Citadel, Horus met with Regulus, the Tech-priest who represented the Mechanicus in the 63rd Expeditionary Fleet and promised to deliver all of the recovered STC databases from Aureus into the Mechanicus' hands in return for the Mechanicus' support for his rebellion. Regulus eagerly accepted the bargain and then offered to serve as Horus' envoy to Fabricator General Kelbor-Hal of the Mechanicus on Mars, offering him both the recovered Auretian technology and greater political autonomy and the right to research formerly forbidden technologies if he agreed to betray the Emperor. Kelbor-Hal ultimately accepted this offer, which would unleash the civil war within the Mechanicus known as the Schism of Mars and lead to the tech-heresy that founded the Dark Mechanicus. In this way, the Warmaster's conquest of the Auretian Technocracy represented the first major step along the path of treachery that would unleash the horrors of the Horus Heresy upon the galaxy.
- False Gods (Novel) by Graham McNeill