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.
- The term comes from the Irish/Scottish Gaelic word geas, which is a curse, spell, or vow.
- Halo: Cryptum (First appearance)
- Halo: Combat Evolved Anniversary (First mentioned)
- Halo 4 (Mentioned only)