Legio Tritonis - Horus Heresy: The ideological splits between the two disparate elements of the Legio Venator were to bring much strife to Arachnus. Like many Forge Worlds across the Belt of Iron, Arachnus kept its intentions and loyalties secretive during the opening years of the conflict. Political factions present on the Forge World called for Arachnus to join the war both for the Imperium and against it, while others demanded it seize the moment and establish a new order with the Forge World at its centre.Matters came to a head when a cadre of senior princeps, who had served for solar decades within the Great Crusade, demanded Arachnus fulfil its duties to Imperium and Emperor or face dissent and rebellion at home. In response, several demi-legios of the Legio Venator were dispatched for the Ny'Drinah Sub-sector, ostensibly in support of the Imperial war effort in the region.Given later events, it is clear such a move was intended to rid the Forge World of dissenting elements, the dispatched demi-legio made up primarily of those who held loyalty to the Imperium over their Forge World.Shortly after Arachnus' apparent declaration of support for the Imperium, communications between the Forge World and other planets halted. Docking manifests indicate that voidships in the employ of the Warmaster Horus' fleets alighted at the Forge World during this time, with inventory records detailing shipments of plasma reactors, Titan-grade munitions and raw materials necessary for the construction of god-engines.The nature of these shipments suggest the Warmaster believed he had secured the Forge World as his ally and worked to swell the size of those Legio Venator elements loyal to Arachnus.In this, both the Imperium and the Warmaster were fooled. Having reaped the benefits of claiming allegiance to both sides, Arachnus broke its silence to announce its independence, declaring both the Emperor and the Warmaster as conquerors and murderers who deserved no respect from the Forge World and its people. A brief period of cleansing followed upon Arachnus, with Legio Venator princeps who refused to break their oaths with the Imperium set upon by maniples of Titans bearing altered colours and assembled under a new banner.In acknowledgement of its new path, the secessionist elements of the Legio Venator rallied under a new name -- the Legio Tritonis, chosen in honour of their Forge World and its two moons, Iktomia and Nizkara. Though warfare between secessionist and Loyalists was to rage on Nizkara, the second moon of Arachnus, for the remainder of the Horus Heresy, the Legio Tritonis had secured the remainder of Arachnus' holdings and cemented its standing as a powerful independent state.The newly appointed wardens of Arachnus were bequeathed two tasks. The first was the total extermination of the surviving elements of the Legio Venator, who were declared as Traitors to their heritage and their ancestral world. To this end, hunter maniples were assigned to the regions surrounding M'Khand, a secondary Forge-fortress appropriated as the primary base of operations for the Legio Venator in the Belt of Iron following the rebellion of Arachnus.Though the princeps of the Legio Venator and the Legio Tritonis had once walked beneath the same banner, neither spared compassion for the other, and death and destruction was visited upon numerous worlds as both Titans Legions sought to eradicate the other.The second task proved to be the expansion of Arachnus' holdings, the Forge World proving ill-content with its current borders. Legio Tritonis demi-legios were frequently reported on worlds bordering the Forge Empire of Arachnus, its god-engines descending upon lesser Forge Worlds who had, in the past, aligned themselves with Arachnus. Portrayed as emissaries for a prosperous new order, any who denied requests for subservience were greeted with fire and flame, populations slaughtered until the worlds bowed to Arachnus.This wanton campaign of conquest and destruction soon earned the Legio Tritonis a new name, for survivors proclaimed that its godengines descended like a tide of darkness, snuffing out all hope.The Legio Tritonis thrived during the Horus Heresy, using plundered resources in conjunction with god-engines captured through conflicts with the Legio Venator and other Titan Legions within the Belt of Iron to rapidly increase its numbers. Eventually, the Dark Tide was to face its reckoning when the Iron Spiders returned to Arachnus with the support of the Legio Atarus. The resulting conflict raged for several standard years and, upon its conclusion, Arachnus was once more brought to heel by the Imperium's war machine.Official records state that all dissenting elements of Arachnus, including the Legio Tritonis, were exterminated to a person. Nevertheless, scattered reports appeared throughout the Heresy of god-engines bearing the colours of the Legio Tritonis, many standing sentinel over concealed Mechanicum enclaves within the Belt of Iron that proved hostile to diplomatic efforts and quick to relocate should efforts be made to conquer them.