Sanctuary 101 was a quiet and remote convent world, a shrine-outpost of the Ecclesiarchy tended by a garrison of the Adepta Sororitas who kept the Emperor's flame burning at the far edge of civilised space. Its cloisters knew only prayer and vigil, and for long years nothing disturbed the devotions of its warrior-sisters upon that isolated rock.
That peace ended in horror when the Necrons rose without warning from the world's forgotten depths. It was here, in the halls of a lonely convent, that the daughters of the Emperor first crossed blades with the ancient star-gods, their bolters and blessed blades set against the remorseless gauss-fire of an enemy that would not stay dead. The Astra Militarum records that reached the wider Imperium spoke of a garrison utterly overwhelmed, its defenders selling their lives dearly against a foe beyond mortal comprehension.
The Sisters of Sanctuary 101 fought to the last, their faith unbroken even as the unliving legions flayed them from the world. Their sacrifice bought precious warning of the Necron threat stirring in the dark, and their doomed stand passed into the martyrologies of the Ecclesiarchy. Sanctuary 101 endures in Imperial memory not as a place, but as a name synonymous with the first grim herald of an ancient and terrible enemy.