Astroengineering (Earth-2042)

Astroengineering is name given to the construction of megastructures in space by technologically advanced beings. It is a form of megascale engineering, but deals with structures that are "easily observable" from interstellar distances astronomical instruments: e.g. a space elevator is an example of megascale engineering, but it is not an example of astroengineering. Notable examples of astroengineering are the Halo rings, built by the technologically advanced Forerunners, as well as the Death Star, built by the Galactic Empire.

Construction of these megastructures are restricted to either Tier Zero, Tier One or Tier Two civilizations.

Source

 * https://www.halopedia.org/Astroengineering