From Destinypedia, the Destiny wiki
The Athenaeum worlds of the Cabal Empire are massive planetary repositories of knowledge and technology. The Vaults contained technology belonging to many species that they either assimilated to their empire or conquered. The vault contained many pieces of technology with terrifying potential. Such pieces include Sentient Anomalies, Thought-powered Reality Smashers, and Portable World Enders. However, it is unknown whether or not the Cabal lost them or deployed them. Emperor Calus himself is unsure as the Loyalists caretakers that he personally stationed on each athenaeum world have been silent for a prolonged period of time.