Shield world

Shield worlds are artificial worlds built by the Forerunners as one of their measures as refuges and military fortresses. Evidently, most shield worlds known today were built during the rapid militarization of the Ecumene that followed the Flood outbreak. Such worlds were used to both to marshal fleets and evacuate regional populations into relative safety from the parasite. Many shield worlds, perhaps the majority of them, are presumed to have been destroyed during the Diluvial War.

Though there are differences between the shield worlds encountered in the modern era, it can be extrapolated that most shield worlds take the form of spherical megastructures on a scale comparable to terrestrial planets. Many feature a habitable outer surface and may be designed to appear as natural planets on all but the closest inspection. Shield worlds include terraformed refugium habitats in their interiors to accommodate both evacuated populations and biological specimens moved out of the Flood's way. These may be fashioned into a series of concentric shells, or as a single miniature Dyson shell surrounding an artificial "star".

Although some scholarly debate exists over the matter, evidence suggests that most of the shield worlds were never designed to withstand the Halo Array's effect, as they were conceived and used at a time when the use of the Halos was not even widely contemplated. An exception to this rule is the shield world Onyx, or rather the Dyson sphere accessed through Onyx's core, which appears to have been planned as the Forerunners' final refuge. The Dyson sphere was locked away in layers of slipspace so deep it may have been possible to escape the Halo effect there, though it is possible this was not fully certain even to the Forerunners themselves.

Known shield worlds

 * Etran Harborage — A shield world previously known to the Covenant, Covenant records released since the war indicate that the Etran Harborage was destroyed under unclear circumstances in the early 2530s.
 * Onyx — A shield world located in the Zeta Doradus system, Onyx concealed a portal to a Dyson shell locked away in slipspace.
 * The Refuge — Home to a divergent population of Sangheili which resumed contact with the Concord of Reconciliation in the post-war decades.
 * Requiem — Known only through cryptic references in Forerunner records, little is known of Requiem at this time.