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Geas is an archaic Forerunner term that refers to a generations-long genetic command imposed on an organism or species. Under the influence of a geas, an organism can be given a set of subconscious orders that will be passed on to their children, in some cases lasting several generations. Only highly skilled Forerunner Lifeworkers were capable of creating a geas.

In approximately 100,300 BCE, Bornstellar-Makes-Eternal-Lasting speculated that The Librarian had imposed a geas on the human race. Forerunner students of the Mantle also hypothesized that the Precursors may have imposed a geas on the Forerunners themselves.[1]


  • The term comes from the Irish/Scottish Gaelic word geas, which is a curse, spell, or vow. 



  1. Halo: Cryptum, page 49

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