Our Emperor, who art set upon the eternal throne of Holy Terra, protect our soul, so that we may retain our humanity and yet not avert our eyes from the abyss of the Immaterium. For we stand watch over these worlds in your name, and for the sake of the souls of your children among the stars. We are weak on our own, but through your will, Holy Emperor, our watch will prevail. And no evil shall pass our guard, no demon touch those worlds blessed by your grace.
- from the Oath of Watchmen upon the Limes Gondwana
On the precipice of the Thetys Rift lie the many thousand forts and watchtowers of the Limes Gondwana, the single largest defensive line of all of Sector Gondwana. These are the walls against which the hordes of the Immaterium break, where the fate of trillions is decided with every loss and victory.
Through systems and interstellar space, the bulwark of the Imperium spans many dozen light years, all along the vast abyss of the Immaterium. To the galactic north, it ends in the fierce clouds of the Glacial Nebula, which not even the chaos fleets can navigate. To the galactic south and west, the Limes reaches beyond even the Erinnyenmere and to the spiral gulf between Subsectors Cambria and Ordovicia, where pandemonium of Chaos reigns.
The Limes is structured in tiers of entrenchment. Highest among these is the First Castellum Mongotiacum, the ancient citadel deep in the Glacial Nebula. It commands directly, the major Castra along the Limes line.
Of these, there are four: Rifersceith, Syburg, and Bilstein. Each Major Castellum, alongside Mongotiacum, serves as home port to one of the Castellum Fleets, and a standing regiment of the Imperial Guard. The Prefect of each Castellum, also titled "First Watchman", bears responsibility for their part of the Limes Gondwana, including the command of several dozen Minor Castra and Star Forts, as well as planetary outposts and the massive number of watchtowers, listening posts, and relay stations.
In the event of a chaos invasion, it is the foremost duty of each Major Castellum, to alert immediately the entire sector and hold off the enemy at all costs, until a counteroffensive can be mounted.
The fleets of the Major Castra are sent to the Limes Gondwana directly at the behest of the Imperial Navy and likewise report directly to the High Admiral of "Battlefleet Gondwana", even though said Battlefleet does exist only nominally. Most importantly, the Castellum Fleets are thus freed of any accountability toward the Triumvirate Worlds and their schemings, acting solely to protect the borders of the Imperium. For the same reason, they will neither interfere in internal conflict nor incursions other than those of the Thetys Rift. Exceptions to this rule have been known in the Sector's History, but only when such orders were given directly after pleads to the High Admiral himself.
Regiments of the Limes Gondwana
Like the Castellum Fleets, the Imperial Guard Regiments of Limes Gondwana are not those raised from within the Sector but sent from worlds elsewhere in the Imperium. Even though they have been stationed for centuries in these constellations, they do not mingle among the worlds of Subsector Cambria, and never come into contact with them, safe for mandatory drafts from the populace of Gondwana, to retain diversity in the gene pool of the Regiments for the purpose of breeding new generations.
Since they have been stationed often in the fifth or sixth Generation since initial deployment, the Limes Regiments have come to resemble neither any force from within Sector Gondwana nor the homeworld they were initially from. Instead, an entire culture of its own has developed among each of them, leaving barely any memory of the world they once left behind.
As a fort unconquered for ten-thousand years, it is the supreme seat of command for the Castellum Fleets and foremost staging ground for the Imperial Navy and Battlefleet Gondwana. Maintaining the highest degree of Isolation from the remaining Sector Gondwana, not even the authorities of the Triumvirate know exactly how large the force is, which has been stationed there. Neither do they maintain regular contact to the officials of the Imperial Navy, safe for matters of utmost importance in the event of a sector-wide invasion.
Even the architecture of Mongotiacum itself is shrouded in mystery since it is always only seen in the deepest folds of the Glacial Nebula, obscured behind clouds of mist and fractured ice.
Lying isolated as the vanguard of the No-Man's-Land of Subsector Cambria, Rifersceith has been the lynchpin for the Limes Line since the loss of the nameless star fort, when Thetys last surged and lashed out against Myriadenburg.
Out of sheer necessity, Rifersceith grew to maintain stronger relations to worlds of Subsector Cambria than any other part of the Limes Gondwana. Closest are its ties to the Forlorn Fortress Gahmuret, with which it shared its fate in many ways. Often fought forces of these two worlds together, alone and declared forlorn by the rest of all the galaxy. And nonetheless, they prevailed, earning them an infamous reputation.
Closest to the Thetys Rift of all Castra lies Castellum Syburg, between the Pantheon World of Mekephau, the Cthonic Fortress Tumunzahar, and the Forlorn Feral World Kumaforth. It is daring fort, prevailing through methods and paths for victory frowned upon by all other worlds. Some go so far as to say the Castellum itself has been tinged by the warp, so fervent are its ventures into the abyss, to reach out to its bridgehead on the Forlorn Feral World, it's ties to the mysterious prophets of Mekephau's Pantheon and the legends of impossible victories earned by its forces.
But the gates of Syburg remain closed to all the world – so none shall ever know what truly transpires in its darkest dungeons.
Although a Major Castellum of the Limes Gondwana, Bilstein is most commonly known as the military capital of the Fiefdom of the Crimson Queen. Officially isolated, through elusive ways, it is in constant contact with the shadow fiefdom and maintains dealings with countless rogue traders. Though secretive, ever speaking only through automaton avatars, the watchmen of Bilstein reveal their strange findings and observations in the Thetys Rift to all who wish to hear them. Their fortress line was never broken, even during the last Surge of Thetys, which has led some to believe they are secretly allied to a mighty power beyond the Thetys Rift, which kept the forces of the Immaterium from their side in check.
Fortress Worlds of the No-Man's-Land
Closely tied to the Limes Gondwana are the Fortress Worlds Tumunzahar and Gahmuret, both of which stand against the tides of the Thetys Rift as the Sector's second line of defense.
Old and lost Worlds
There are remnants along the Limes lines, of worlds existing prior to the Imperium's coming to Sector Gondwana. These Old and Lost worlds are on no star map anymore, forgotten by the chroniclers of history, for all their erstwhile wealth and power veined and dissipated in the vastness of time.
But the Watchmen of Thetys remember and maintain small outposts were once mighty cities were. On the ruined worlds without names, the soldiers of the Limes Gondwana gaze at the ruins of old and wonder what ancient wonders may be hidden underneath.
The Coming of Trantor
The Limes Gondwana as such first arose under the authority of the Triumvirate World Trantor. Most of the watchtowers and castra were raised during this time when the Great Crusade had just halted and mankind entrenched itself on the frontiers of the Imperium. These Millennia, often painted now as an ancient golden age, were in truth cast in the everlasting light of desperation and the expectation of coming doom. The Horus Heresy shook the galaxy and brought the war to the young defenses. Since then, their test has never ended.
Once the Castra had gained strength enough to stand on their own, and Gondwana was recognized as the outermost frontier by the high and mighty of the Imperium, the Limes Gondwana was granted a standing of its own and its bulwarks were strengthened once more. From the might assembled along with these stars, hubris grew. And so the forces of Gondwana stood ready, waiting when the Shadow of the Thetys Rift grew tall.
The Surge of Thetys
Once Thetys Surged, it broke the line, and many forts faltered in the invasion's wake. The defenses of Subsector Cambria were swept away and the Castra of Limes Gondwana found themselves surrounded deep in hostile territory. All Major Castra were besieged for the duration of the Thetys Surge. Even Mongontiacum, the citadel of the Glacial Nebula, had to withstand a centuries-long onslaught of corrupted enemies. During this war, the Major Castellum, of which the name will never be spoken, fell to the demonic fangs of the Immaterium and had to be destroyed. The other Castra persisted but were reduced to lone outposts of humanity, insignificant to the larger war.
Great shame was brought upon the Limes Gondwana on that day, and one standing regiment of the Limes Guard committed mass suicide once the battle was concluded, for they would not bear the shame of having been defeated.
Old power reasserted
Following the end of the Thetys Surge, Gondwana was to be rebuilt stronger and mightier than it had ever been. To the Imperium in its state of constant decay, the prospect of creating something unsurpassed in its strength in history was nearly inconceivable. But resources of the Mechanicum of Mars, of the Imperial Navy and all Triumvirate Worlds were channeled to strengthen the defense of Subsector Cambria, creating a vast frontier defense the likes of which is unique in the galactic region. Countless new forts and orders were founded, redundant auger systems and relay networks were put into place, and entire populations were raised to provide a worker populace to the great machinery of the Limes Gondwana reborn.
A new shadow falling
At the dawn of the 41st Millennium, a new shadow grows within the Thetys Rift. And this time, the forces of Limes Gondwana will not simply stand to wait. Calls for aid have been sent throughout Sector Gondwana and far beyond. From the old homeworlds of their regiments, the Castra call forth reinforcements by the billions. The Imperial Navy has been called upon, to raise a true Battlefleet Gondwana and sent forth the Imperial might against the coming storm. In the wake of long millennia awaiting the second coming of the Thetys Surge, the Limes Gondwana gathers its strength once more. A new war is coming.
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