"Shamans of ancient Terra once used the warp as a conduit for their power, without knowing what it was. Now, our librarians use it for more potent abilities, yet their understanding still has not apexed. We seek to change that."
―Grand Elocutor Gerrel, to Legion Master Korrus the Machinist of the Yttrium Titans.
As the Space Wolves Legion decended upon Prospero, the Great Wolf ordered 100 Astartes be captured alive and brought to the Emperor for judgement. And so he did. He brought 100 Thousand Sons astartes to Terra, and the High-Lords reverse engineered their gene-seed to make a new legion. The Beholders were born from the ashes of Prospero, and now seek to either make their Primarch Magnus the Red attone for his betrayal, or bring him back into the light of the Emperor. During the Nova Terra Interregnum, the legion was offered a place among the ranks of the seccesionists, but decided to wait until a clear outcome for the movement had been foreseen. In the aftermath, the legion joined the Nova Terra Regency along with their brother legion, the Yttrium Titans.
Faeron Sigma (More commonly known as Faeron) is a small moon of a gas giant called Faeron Prime. It is a barren and craggy world that is shared with their brother and friend legion the Yttrium Titans. The Titans mold the land so that the Beholders can build their libraries and monasteries.
The capitol city of Faeron is Demord. Living on opposite sides, the two legions take turns safeguarding the peasants living in the city with them, with the Beholders being given the title of Daywatch, and the Titans earning the name Nightwatch.
Derived from Magnus the Red, their gene-seed has high traces of Warp-connectivity, allowing the legion to have a high number of Psykers when compared to other legions. Virtually every Astartes in the legion has some connection to the Warp, however small.