[Lord Commander Erus]

all this talk about the Sisters of Battle inspired me to dig through my brain and books and post this up for you guys. It's a theory I've pieced together from various concrete bits of fluff, inference from articles, etc.. All that is stated WAS said in a White Dwarf, A codex, a Book, or something. Just don't ask me which, as I am NOT journeying back to my mentors place and delving back into his stock again!

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The Sisters of Silence were pariah gene carrying women who were highly trained and given equipment and armor simlair in power and look to the custodes, but not gen-hanced (and I mean GEN-HANCED, not implants) like they were. They were left natural, un enhanced except in grave injuries and powered by rejuvenate treatments to keep them fit and young. This was done rather deliberately to prove the right of humankind to rule the galaxy as the most supreme being. Because, enhanced as Marines and Custodes, or left to Nature (Sisters of Silence), Man will conqeour all.

The Sisters of Silence are to the Sisters of Battle as Custodes are to SM, the bad ass, deadly forerunners.

The Sisters of Silence died mostly in the Siege of Terra fighting in the Webway Gate the Emperor lost control of. Fighting to keep daemons out of the Palace itself, a task their shared pariah genes made them most adept to. After the siege, most of the Sisters were dead, and the rest are theorized to have disbanded or broken apart in shame at their failure to protect the Emperor.

From here it is sketchy, but spotty bits of fluff hint that the Brides of the Emperor, and other various all female groups of elite, but enhanced warriors, were trained and used mainly on Terra only to honor the Sisters of Silence, and as palace and elite guard on Terra outside of the Throne Room where the Custodes had confined their might to. These warriors were not pariahs however, as the decimation of the Sisters of Silence saw the gen-marker become an even rarer occurrence. The gathering of so many females (females in genetics usually pass on psyche related genes more so than a father, thereby the pariah gene in them would be dominant) bearing the gene who died without progeny ensured the near mythic rareness of a Untouchable.

After the Age of Apostay, it was seen that such highly trained martial traditions (if indeed the various groups were splinters of the Sisters of Silence, then they would have undergone much the similar elite training, but it would have changed just as Space Marine traditions and training did) running independent of the High Lords and the Imperiums DIRECT control was dangerous, so they were all collected and formed together, and split into Orders.

Leading theory and hints I can find is the Orders we know (Bleeding Chalice, Sacred Thorn, etc..) today were, (in respect to the FIRST ones) named after the original organizations of these fighting women, who indeed took those names from their fore-runners hearkening back to company and squad names of the Sisters of Silence themselves. They were put under the control of the Inquisition namely because of the massive betrayal they wrought under Vandires command, and in part their awe inspiring faith and fervor stem from a desire to erase their dishonorable and blood stained past.

Not official, but following all published GW fluff and pasting it together in a non contradictory document, there ya go!