Imperial Palace - Defences of the Palace: The Emperor's palace on Terra is the largest and most impregnable defensive structure in the Imperium. It sprawls across an entire mountain range, stretching for thousands of Terran kilometres over the surface of the Throneworld.The Adeptus Custodes are responsible for the defence of this immense fortress, a duty they discharge with tireless diligence.In the days of the Great Crusade, the Imperial Palace was a surpassing wonder of engineering. Yet the necessity to fortify that beautiful structure against the baleful intentions of the Warmaster Horus -- and the subsequent widespread devastation suffered at the hands of his Traitor hordes -- wrought irrevocable changes. In the wake of the heresy, the Imperial Palace was rebuilt as the mightiest fortress in Human history.The ten millennia since have seen it become ever more bloated, polluted and immense. The palace's former asceticism lies buried beneath strata of Gothic ornamentation and the brutal grandeur of the Cult Imperialis.What once was bright and magnificent is now vast and lowering, a hunched architectural monstrosity that wears its martial might like a challenge to the terrors of the darkling void. There can be no clearer metaphor for the fate of the wider Imperium, but though the palace is a grotesque mockery of its former self, still the Custodes guard it well.This is no small task. The circumference of the palace's outermost walls is measured in thousands of kilometres. The towering spires of its macro-habs and spaceports break through the atmosphere and rise into the void like the spines of some bioluminescent beast.Its sub-levels dig deep into Terra's holy bedrock, in some places reaching a depth of hundreds of kilometres below the surface. Its corridors, chambers, vaults, fastnesses and plazas are so multitudinous that no single record remains to list them all, and the societal sub-nations, clan holdings and techno-urbanic serf tribes that dwell within its walls could populate entire star systems.Despite this, the Adeptus Custodes have always proven equal to the duty of overseeing the palace's defence. It is they who patrol the colossal and seemingly endless walls, who stand guard over the sanctums and armouries, who patrol the petitioners' highways, the famed spaceports and the vast fortifications.They inspect the endless kilometres of orbital guns and defensive silos, and maintain a wary guard over the hidden vaults deep within the palace which contain secrets so dreadful that they could bring about the fall of Humanity were they ever released.And yet, the Adeptus Custodes find the manpower and dedication to do so much more. For thousands of Terran years, their Shield Hosts have mustered in secret and set out aboard requisitioned warships to strike down threats identified by the roaming Eyes of the Emperor.Bands of Custodians have regularly patrolled the Sol System, serving as rotating garrisons for military facilities based around Luna, Venus, Pluto and numerous deep-space star fortresses that watch the approaches to Terra.The Adeptus Custodes have also long liaised with the Imperial Fists Space Marine Chapter, who still maintain their role as joint guardians of the Sol System, and whose immense star fort -- known as Phalanx -- has often held a protective orbit over the Throneworld. The Adeptus Custodes have remained unwavering in these duties for thousands of Terran years.Now, even as the galaxy darkens around them and new wars arise for them to fight, they are more determined than ever to ensure the Imperial Palace, and the whole of Terra, stand inviolable.