Each Dominion, numbering a hundred Sisters under the command of an Oblivion Knight-Centura, has its own heraldry, traditions and mute-vows, but all are loyal to the Imperium. Some are charged with specific duties – such as infiltrating the hyperspatial tunnels of the Webway to stymie the plans of psychic xenos races, recovering pariahs from enemy forces that seek to use them for their own gain, or neutralizing spectral attacks in strategically vital locations. Others have carte blanche to pursue their own agendas, provided they serve the collection of the Great Tithe or the destruction of the Great Enemy’s forces.
The Silent Sisterhood maintain a strong presence both on Terra itself as well as notably at their headquarters in the Somnus Citadel on Luna - a facility handed over by the ancient Selenite cults - and the Magadan Orbital Construct - the fortified orbital anchorage station utilised by the League of Black Ships in the Sol System to deliver their cargo, and forbidden to all others. Nevertheless, much of the initial sifting and processing of the Great Tithe takes place not in the Sol System but elsewhere on scores of isolated, backwater, and otherwise prohibited star systems in every Segmentum - an understandable change from the tithe's early days given the sheer scale of the operation as the Imperium has expanded and the potential security risks involved in so many untrained psykers being concentrated in a single area.
These Divisio Astra Telepathica administered star systems are only known to other arms of the Imperium as vague and shifting code designations such as Star One, Silent Harbour, Taceant Astra, and Kamiti Sona. Here the Silent Sisters alone hold sway and what numbers, facilities, and resources they possess in these sovereign domains, none save they and the Emperor know. In fact, such is the shroud of secrecy surrounding the Great Tithe that only the Navigators of the League of Black Ships know the location of these processing worlds and various Black Ship anchorages, collection-node stations, and outposts scattered across the Imperium, and their lives are led in sealed biome-crucibles, prisoning homes which auto-incinerate all within should their seals ever be compromised; such is the priceless wealth in human potential of the Great Tithe judged and guarded.
- The Horus Heresy Book Seven: Inferno and Codex: Sisters of Silence 7th Edition