Orion Complex

The Orion Complex, known in Covenant astronomy as the Hial-Achor Gathering, is a prominent molecular cloud complex and star-forming region hundreds of light-years across. One of the most distinctive features of the Solar Region of the Orion Arm, it is part of the Radcliffe Wave, an undulating string of molecular clouds that runs through the Orion Arm. It is located in relative proximity to Sol, at around 1,100-1,400 light-years away.

Since the mid-2550s, the Orion Complex has been associated with increasing confidence with the Forerunners' region of origin, referenced in some records as the Lothean Complex. Known to the Covenant as the Sacral Cradle, the Complex is revered in Covenant scripture as being home to the Forerunners' cradle-worlds and the heart of their Bygone Ecumene. It is still not known with definite certainty whether the Lothean Complex is in fact the Orion Molecular Cloud Complex — other candidates brought forward include the Taurus and Perseus molecular clouds, as well as various stellar nurseries along the Orion Arm. However, astronomical cross-referencing of various Forerunner and Covenant sources conducted since 2553 strongly suggest a correlation with the Orion Complex. Even so, it remains vague to what extent the Forerunners' definition of the complex's boundaries corresponds to modern human astronomy; there are some indications that the Forerunner definition originally encompassed a much larger region of space than the molecular cloud complex proper.

The complex is vast in scale, comprising many large nebulae and numerous lesser interstellar clouds, and tens of thousands of stars. Its most prominent features are the giant molecular clouds Orion A and Orion B, which are in turn composed of various smaller nebular formations. It also includes the Orion OB1 stellar association, the Lambda Orionis Molecular Ring, and the Orion-Eridanus Superbubble, formed from various supernova remnants including Barnard's Loop.

History
The Forerunner civilization supposedly originated in or near the Orion Complex. This is corroborated by some archaeological evidence, with some of the oldest Forerunner remnants being discovered around the region. Evidence suggests that a number of artificially-induced stellar disasters exiled the Forerunners from the core regions of the complex, focusing their colonization antispinward along the Orion Arm, with them settling worlds in and around the molecular clouds of the Radcliffe Wave.

During the Forerunners' war against the Flood, a set of core worlds, evidently near the Orion Complex, served as their final line of defense. As the parasite spread rapidly throughout the galaxy, the Forerunners effectively gave up trying to defend worlds outside their core worlds, defined by the Jat-Krula array or the "Maginot sphere" as rendered by some Forerunner auto-translators. During this time, numerous once-bustling megalopolises in the region were razed as part of scorched-earth tactics by the Forerunner fleet in an effort to halt the parasite's spread.

Due to its prominence in the Orion Arm, the Covenant have long known of the Orion Complex as an astronomical formation. The earliest known observations of the complex were in pre-Covenant Sangheili astronomy. The Sangheili named it the Hial-Achor Gathering, after the nebulae known as Erum Hial, which form part of the complex, and the classical Sangheili constellation of Achor, as the two overlap when observed from the Urs system. However, it has not even up until this point been conclusively verified as being the Forerunners' cradle.

The Covenant always had some idea of the existence of a Forerunner core region, as well as said core being based in or near a prominent molecular cloud formation, but its exact location remained elusive to this day. The Covenant had many names for the region: the Cradle of the Gods or Cradle of the Ancients, the Sacral Throne, the Divine Abode, the Holy Cradle, and so forth. Arcane scriptures spoke of the "fabled throne-realms of the ancients nestled in the grand embrace of shimmering clouds of primeval stardust", and many believed it to hold unimaginable treasures, not in the least the legendary Forerunner throne-world, Maethrillian. Over countless generations of Covenant history, numerous explorers claimed to have found the Sacral Cradle; yet its exact location remained undetermined as the Forerunners had many centers of activity and population, each as or more impressive than the last, and intact records or star charts were sparse. The Covenant had begun to encroach on the actual Orion Complex by the later centuries of their history, though even then there was uncertainty and debate as to whether this truly was the Cradle. Further complicating matters was the increasing frequency of Line installations toward the core regions, which made any progress slow and nearly stopped it under certain administrations. This was in addition to the navigation anomalies formed around the dust clouds of the complex.

More often than shining citadels and magnificent engineering feats, however, the Covenant's explorers beheld only the terrible devastations wrought by the Parasite: entire systems ground to rubble, the detritus of prematurely detonated stars, and scores of planetary ecumenopolises rendered cold and dead. There would be some scattered treasure to reclaim, locked away in silver orbs of slow time or beyond impenetrable illusions and unnatural angles; but all too often explorers found only empty husks of once glittering star-citadels; planetary systems woven with vast orreries of interlocking orbital rings and intricate tapestries of thousands of artificial worlds now hollow and lifeless, or haunted by fell machine-ghosts and the babble of morbid eulogies; geometries once elegant twisted into nightmarish mockeries, their self-repair systems corrupted by the Flood's multi-vector assaults, and data vaults either corrupted or unraveled by the Forerunners' own firebreak viruses. And there were dangers: defensive sentinel networks; runaway nanotechnology or hostile megaengineering machinery; degraded or corrupted remains of ancillas and lower-order automatons; traps and automated systems.

There are hundreds of navigation hazards, cataloged and otherwise, in and around the Orion Complex. For one, molecular clouds such as the Orion Complex are notoriously difficult to navigate due to density of material therein. In addition, artificial hazards abound. Aside from the Jat-Krula, there are still-active secondary slipspace interdiction systems and other higher-dimensional disruption machinery. And it is not just Forerunner defenses the Covenant were forced to look out for, but the workings of the Enemy: lesions and other undefined volumes of damaged space-time remain throughout the entire region.