The Basilica Mortis is home to the Mortifactors. The ancestral home of the Mortifactors Chapter of Space Marines rotates slowly in the wan light of Posul and her faraway sun, its surfaces craggy and mountainous. For nearly ten thousand years, since the Chapter's founder, Sasebo Tezuka, had been led here by the Emperor's tarot, the Mortifactors have stood sentinel over the night world of Posul, and since that time, these holy knights of the Imperium have trained members of their warrior order within the walls of their orbiting fortress monastery.[Needs Citation]
In appearance, it resembled some vast mountain range cast adrift in the void of space. The Imperium's finest tech-priests and adepts had come together to create this orbiting fortress: the Basilica was a marvel of arcane technical engineering that had long since been forgotten.[Needs Citation]
At full occupation, the monastery is home to the thousand battle-brothers of the Chapter and their officers, with a supporting staff of servitors, scribes, technomats and functionaries that number seven and a half thousand souls.[Needs Citation]
Within this mighty fortress monastery the gently arched walls are smooth and spartanly ornamented. Here and there along their length, tiny niches are lit by delicate, diffuse lights, held stasis-sealed vessels containing some of the Chapter's holy relics. The halls of the Mortifactors are gloomy and silent as a tomb. Every portal and chamber a visitor passes through bears more skulls and upon closer inspection, only then, does one realize that none of them are carved or fashioned by human hand. All are real, bleached and dusty with age.[Needs Citation]
The Gallery of Bone is the main audience chamber of the Chapter Master of the Mortifactors. It is aptly named; a carved cloister of bone surrounding a stone flagged floor paved with hundreds of tombstones. Niches set within the columns of the cloister contained skeletal warriors clutching swords and the entire, domed ceiling is formed from interlocked skulls, their eyeless sockets glaring down at those who stand within their domain. Mortuary statues of angels flank a vast throne composed of the bones of long-dead Space Marines. Everywhere one looks, death is venerated and exalted above all things.