Trilla was first discovered by humanity during the Great Crusade when the Alpha Legion brought the Emperor’s light to the Anargo sector.  Three Imperial Army divisions were left behind to defend the world and to supervise its colonisation, with the majority of the colonists coming from other more populated worlds in the sector.  At the time of the Horus Heresy the population was still small but the fledgling colony was at least largely self-sufficient.  As a result of its small population and low importance Trilla was spared any outside attention during the great conflicts of that time, it did however suffer from an internal schism.  The world’s Imperial Commander, a man by the name of Alec Thrand had always resented being left behind on Trilla and during the Horus Heresy the aging commander saw his opportunity to conduct one last campaign and maybe carve himself out a little piece of the Anargo sector.  Unfortunately for him his rebellion never made it off the planet, the commanding officers of two of the Imperial Army divisions mutinied against his rule to remain loyal to the Emperor and while Thrand’s own division was able to surprise them and inflict significant casualties the other two divisions eventually won the brief war.  Thus when the Ultramarines arrived in the sector to liberate it they found a world loyal to the Emperor and largely undamaged, albeit with a somewhat depleted defence force.

During the rebuilding after the devastation of the Horus Heresy the decision was taken by the new Priesthood of Terra to develop Trilla, a highly fertile world that still only had a population of around 3 million, as an agriworld to provide food to support the reconstruction efforts and the growing populations of other worlds in the sector that were no longer self-sufficient.

In the early years of the Age of the Imperium the Cult Imperialis spread rapidly in the Anargo sector, especially so in the Dorvastor sub-sector, with Trilla being no exception.  The Imperial church developed a strong hold on Trilla, the largely poorly educated farm labourers proving very faithful adherents, and like most of the rest of the worlds in Dorvastor sub-sector Trilla became closely tied to the world of Dorvastor.  The close ties between Trilla and Dorvastor continued through the period of the Shrine Wars, indeed the presence of an agriworld nearby aided Dorvastor as it enabled Dorvastor to continue to feed the vast masses of pilgrims it received despite the conflicts with Cirrus I.

In late M35 the Adeptus Mechanicus in the Anargo sector were working on developing vaccines against orkoid related organisms and infections in the hopes of purging some of the thoroughly Ork infested worlds in the neighbouring Cruciatine sector and aid the reclamation of that sector.  Unfortunately something went wrong during the development process and resulted in the production of a virulent strain of parasitic micro-organisms.  In the normal way this would have been bad enough, setting back the war effort in Cruciatine and sending the vaccine program back to first principles but to make a bad matter worse there was a failure in the bio-security protocols of the Officio Medicae leading to the distribution of parasite infected livestock that were used in the vaccine trials to dozens of worlds across the Anargo sector, particularly in the Dorvastor and Meksum sub-sectors.  It is believed that the security failure began with the infection of a number of key members of staff at the principal facility working on the vaccine, who then before the infection became apparent, but still with their judgement and decision making impaired, made a series of blunders involving the disposal of the livestock used in the trials.  Whatever the root cause the end result was a devastating plague that came to be known as the Vulticus Epidemic after the Vulticus facility, the principal laboratory involved in the vaccine development.  The epidemic killed billions over the course of a decade, on Trilla the parasite spread from a batch of infected livestock to almost the entire grox population of the world.  While it was managed to keep the infection in the Trillan populace largely to a minimum, partly due to the low population density on Trilla, this lead to the total quarantine of the world for several months and the cessation of all livestock and meat exports and a human travel ban on Trilla for over 6 years as well as the slaughter of almost the entire Trillan grox population.  This seriously damaged the economy of Trilla as well as that of the Dorvastor and Meksum sub-sectors and indeed the Anargo sector as a whole for many years to come.

Though not a key asset the allegiance of a fairly productive agriworld continued to benefit Dorvastor during the Age of Apostasy as it enabled the Cardinal world to threaten food supplies to high population worlds that were considering rebelling.  When war eventually broke out significant quantities of Trillan food was then channelled into supporting the armies of the Anargo-Dorvastor alliance.  Being little more than a puppet of the Dorvastorian cardinals when Terran forces enforcing the Thorian reforms arrived in orbit the Trillan government quickly capitulated and offered up the senior clergy on the world that had enforced Dorvastor’s will as a token of their supplication.  The Terran forces did also insist on the execution of a small number of other senior government officials, placing Trilla under the direction of the Administratum, but largely accepted the world’s capitulation.

In the rebuilding following the Apostate wars the Adeptus Mechanicus of Proteus appealed to the Administratum for governance of Trilla, citing the damage that had been done to many of the sectors agriworlds while Trilla remained unharmed and claiming that they could rapidly increase agricultural output by at least 50%.  It was understandably believed by the Administratum and others that a considerable proportion of the driving force behind this appeal was a desire to further snub Dorvastor and the Ministorum.  Not objecting to a further breakup of Dorvastor’s power base, but not wanting to entirely cede control of an agriworld to the Adeptus Mechanicus the Administratum proposed a compromise option in which the Administratum and the Mechanicus would share the governance and production of the world, with most of the Mechanicus’ share of production coming from increases in output they instigated.  The priesthood of Mars agreed to the Administratum’s compromise deal, as did the majority of the people of Trilla, who were also keen to distance themselves from Dorvastor.  The Adeptus Mechanicus held true to their claims changing Trilla from a moderately productive agriworld to one of the most productive agriworlds in the sector.  This, as hoped did indeed aid the reconstruction of the sector, and in particular the Archaios sub-sector, where most of the Adeptus Mechanicus’ share of production was sent.

Over the years the influence the Adeptus Mechanicus holds over Trilla has increased with much of the population moving to a faith more based in the Omnissial traditions of the Cult Mechanicus, though at the same time as a result of the new policies introduced by the Mechanicus the population shrank quite considerably.  The increasing influence of the Adeptus Mechanicus over Trilla has never sat well with the Cardinals of Dorvastor and in more recent times when the Ministorum has recovered some of its reputation and respectability Dorvastor has been more willing to express its irritation with the situation.  As such the Trillan issue has continued to be a sticking point in relations between the large scale organisations of the Adeptus Mechanicus and the Ministorum in the Anargo sector.  The Administratum is technically neutral on the matter, but is also keen to ensure that Trilla maintains its current levels of output, which would likely be impossible without the extensive involvement of the Adeptus Mechanicus.  This has meant that the Cardinals have had to satisfy themselves with offering covert support to those elements of the Trillan population that rebel against the growing fellowship of the Cult Mechanicus on the world.

In 340.M39 a radical separatist faction of the Adeptus Mechanicus created a cyber-virus known as the Kappa-strain designed to take control of enemy servitors, cogitator banks and other technological devices.  The separatist researchers had had only a weak hold over the virus at its inception and it soon began to evolve out of control eventually becoming the Sigma-strain, which had unexpected effects on servitors, corrupting control mechanisms, stimulating independent thought and frequently leading to cognitive disorders.  As soon as the main leadership of the Adeptus Mechanicus learnt of this the faction was immediately declared to be tech-heretics, rounded up and executed with their works destroyed.  The cyber-virus was nearly contained, but the heretical researchers had not quite been caught in time and a small number of the researchers escaped immediate capture taking some infected servitors with them, and in the confusion surrounding their escape some servitors escaped into the environment.  On a number of worlds small numbers of servitors went on the rampage as they became infected with the Sigma-strain destroying installations and technological devices around them, spreading the Sigma-strain to other servitors, machine spirits and cybernetic organisms.  One of the escaped researchers fled to Trilla, hoping to take refuge with their presence masked by the large representation of the Adeptus Mechanicus on the world.  Before they were caught they continued for a short time to attempt to refine the cyber-virus and managed to infect a processing plant in Pantomel and a number of the multi-harvesters operating out of that city with the Sigma-strain causing a considerable amount of havoc in and around the Trillan capital.  The infected servitors and machines were brought under control and purged but the incident put a noticeable dent in the agricultural output of Trilla for that year.