Precursors (Earth-4001)

"We are the last of those who gave you breath and form, millions of years ago. We are the last of those your kind defied and ruthlessly destroyed. We are the last Precursors. And now we are legion."

- The Gravemind to Catalog in the final years of the Forerunner-Flood war

The Precursors were an advanced race that preceded and were mythologized by the Forerunners and the Glatorian, the latter knowing them as the "Great Beings." The Forerunners classified them as "transsentient" beings, having the ability to travel among galaxies and accelerate the evolution of intelligent life. While the Precursors themselves had long since disappeared during the time of the Forerunners, evidence of their technological and architectural achievements remained scattered across not only the galaxy but also outside it, namely in the Large Magellanic Cloud.

History
The history of the Precursors is a fusion of their mainstream counterparts' and the actual Great Beings' from Bionicle.

Forerunner Beliefs
The Forerunners knew few concrete details about the Precursors, and most of their supposed knowledge came from the mythology they had constructed around their creators. Their most central belief was that the Mantle (the role of guardianship of the galaxy and of all life) was bestowed upon them by the Precursors. From a Forerunner perspective, the passing of the Mantle secured the Precursors' legacy in the form of the Forerunners, continuing their work after they departed, much in the same way humanity was appointed to be the Forerunners' inheritors shortly before the activation of the Halo Array. According to Forerunner belief, the Precursors had peacefully passed away after they fulfilled their mission in creating the Forerunners. The Forerunners believed the Precursors had shaped the Forerunners in their own image, and some even suggested that they may have done the same with humans. By the time of the human-Forerunner wars, prehistoric humans also claimed to be the sole inheritors of the Mantle, something contemporary Forerunners considered heretical.

The majority of this information was mythology with a dubious historical basis, providing a set of explanations for the innumerable mysteries surrounding the Precursors. The facts were very different from what the Forerunners had ultimately chosen to believe.

Technology
Precursor technology was extremely advanced, to the point that the Forerunners labeled it Tier 0, or "Transsentient". Precursors based their technology upon what Forerunners called neural physics: the concept that inanimate matter and thought are inextricably linked and that the universe itself is effectively a living entity. By drawing from the fundamental energies of the universe, the Precursors built exotic, virtually indestructible architecture and traveled across interstellar distances using a superluminal transit mechanism based upon the same principle. It was believed by Forerunners that the Precursors also used neural physics techniques to construct artificial planets and star systems, with Charum Hakkor believed to be one such planet. The Precursors traveled between worlds in vessels that used incredibly advanced artificial intelligence constructs known as knowledge engines and walked upon star roads. The Halo Array, being neurological weapons, are one of the only ways to destroy or otherwise damage Precursor artifacts. This was first evidenced when Charum Hakkor was used as a testbed for one of the Halos: the weapon's firing shattered every Precursor artifact on the planet. This also explains the lack of any Precursor ruins in modern society, as most, if not all, were destroyed when the Halo Array fired and sterilized the galaxy at the end of the Forerunner-Flood war.

Some Precursor artifacts were known to precede the Forerunners by hundreds of millions of years and, being impervious to conventional forms of damage, were durable enough to survive being cycled inside planets' crusts by plate tectonics. Precursor artifacts were often encountered by Miners, who obtained and recorded them but rarely held any particular interest in them. The most coveted Precursor artifact among the Forerunners was known as the Organon, which was allegedly capable of activating all other Precursor artifacts. In truth, the Organon was a Precursor knowledge engine known as Abaddon, who served as the overseer and guardian of the Domain. Although incorporeal, Abaddon was capable of interacting with the physical world in various ways, even vaporizing corporeal beings at will.

The Precursors also left behind a small number of mysterious deep-space artifacts known as "anchors" — large, anomalous masses which released no radiation. They were generally regarded as unstable and dangerous; the Forerunners had recorded strange phenomena near the masses, including ships vanishing and surviving crews suffering severe mental trauma, requiring extensive proto-geometric therapy to restore their minds' neural topology to its normal state. Precursor construction was gray-silver in color, much like that favored by the Forerunners. When witnessed in a collapsed state on Charum Hakkor, the construction material had shattered along crystalline planes. The Precursors also built cyclopean laboratories described as being made of "crystallized reality."

Among the most impressive of the Precursors' structures were the enormous orbital arches and star roads, unbending filaments woven into the fabric of reality which were used to connect entire worlds and star systems. These structures were once plentiful in the galaxy, forming graceful curves across many star systems. They appeared to be mostly dormant and unchanging, apart from automatic adjustments based on changes in planetary orbits. Other types of Precursor constructs included structures referred to as planetary fortresses and citadels. Toward the end of the Forerunner-Flood war the Flood began to reactivate and employ these formerly inert Precursor artifacts against the Forerunners, being able to control them due to its Precursor origins. These artifacts (mainly star roads) were what eventually turned the war in the Flood's favor as they were capable of effortlessly either outright physically tearing apart Forerunner fleets or remotely deactivating their weapons, ancillas, and shields, rendering them helpless against the Flood.

The Precursors' rekindled might extended beyond the mastery of technological artifacts. After reaching the Key Mind stage, Flood compound minds gained the ability to tap into neural physics and along with it the Precursors' reality-mutation capabilities. When moving across the galaxy, Flood-controlled Precursor constructs would convert space-time itself to be unsuitable for Forerunner slipspace drives due to the differences between the slipspace travel used by the Forerunners and the Precursors' neural physics-based transit. Ships using this form of superluminal travel would momentarily radiate multiversal residues accrued during the journey upon return to normal space. The Forerunners suspected that the Precursors possessed unknown means of correcting causality other than the reconciliation Forerunner ships were subject to. The widespread use of neural physics transit affected the galactic-scale magnetic fields that marked the borders of the ecumene's themas. The effects of the Precursors' manipulation of space could even be felt by individual beings; toward the end of the Forerunner-Flood war Forerunners began to perceive starlight as possessing a hostile, repelling quality.

Perhaps the Precursors' most extraordinary creation was what the Forerunners knew as the Domain: a vast reserve containing the totality of the Precursors' accumulated knowledge and experience - amounting to a hundred billion years, with most of the information gathered originating from the beginning of the universe if not earlier. This reserve of knowledge was contained in Precursor constructs in the Milky Way galaxy and projected a massive field through which the records could be accessed anywhere regardless of locality. The Domain itself was also a conscious entity, although this only became apparent to most Forerunners near the end of the Forerunner-Flood war. The Domain would later be discovered and appropriated by the Forerunners as a store of their own records and knowledge, becoming a principal element of their culture. Despite this, the Domain remained highly esoteric to the Forerunners; not even its origin and true nature were known. With the activation of the Halo Array and the galaxy-wide unraveling of Precursor neural physics, the Domain and all knowledge contained therein was lost along with all Precursor architecture. While a group of surviving Forerunners later managed to reactivate the Domain, it remains unclear how much of the knowledge it once contained has been successfully recovered.