Sanctuary 101 was the site of first open contact between the Imperium and the Necrons, in 897.M41. The Necron Sautekh Dynasty led by Phaeron Imotekh the Stormlord took part in the attack. Despite a valiant effort and attempting to preserve all records that they could on these new enemies, all the Sisters inside the Sanctuary were killed and had their skin flayed by the Necrons. Video picts were recorded during the battle, but only showed the Sisters being cut down by flickering shadows. After the massacre, the Inquisitors who viewed the pict recordings realized the scope of this new threat.
"Sanctuary 101" may refer to Room 101 in the novel 1984 by George Orwell, in which the antagonist O'Brien responds, when asked what is in the room, that "The Thing in Room 101 is the worst thing in the world."