From Halopedia, the Halo wiki
Constraint fields are a form of energy field used by the Forerunners to restrain individuals. Warrior-Servants were capable of generating and manipulating constraint fields at will. Higher-ranked Warriors, such as the Ur-Didact, could control these fields to the extent they could be used in a manner similar to telekinesis, allowing the Didact to immobilize and move his opponents from a distance.[Note 1] Constraint fields could also be used for other purposes. For example, Glory of a Far Dawn used two constraint fields to secure Bornstellar Makes Eternal Lasting and Splendid Dust of Ancient Suns as they escaped the Forerunner Capital during Mendicant Bias' attack. These fields were sealed against the vacuum of space and could be merged with one another.
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