The secrets of Grav-weaponry construction are known only to a precious few; their design is based upon the graviton weaponry many Space Marine Legions employed during the Horus Heresy era in the early 31st Millennium. The blessed technology used to craft these wondrous weapons remains a safely guarded secret of the Adeptus Mechanicus, passed on only to those Techmarines who have proven their devotion to the Machine God through centuries of war. This is the way it has been since before the time of the Horus Heresy, when large numbers of these weapons were created, then called Graviton Guns, and used extensively among the Space Marine Legions. The knowledge required to maintain such a weapon is as rare as the knowledge required to create them, and for this reason Adeptus Astartes Chapters se