Forerunner

The Forerunners were an ancient civilization of technologically advanced beings who disappeared from the galaxy around 100,000 years before the present. Their feats of technology, architecture and megascale engineering are still without parallel, as demonstrated by many artifacts and installations that remain throughout the known galaxy. The Forerunners' interstellar empire was known as the Ecumene and encompassed millions of worlds at its height. The Forerunner civilization came to an end after they encountered an extragalactic alien parasite known as the Flood; after three centuries of desperate war, the Forerunners activated a galactic network of superweapons known as the Halo Array as a last resort, wiping out all life in the galaxy. What became of the surviving Forerunners, if there were any, is uncertain.

Though merely one of many long-passed galactic civilizations, the Forerunners are the best-known of them all due to the prominent position they once held. Evidence of the Forerunners' civilization and technological prowess would later be discovered by younger races, some of whom would come to conclude those artifacts could only have been forged by divine hands. Such beliefs eventually gave rise to the alien theocracy known as the Covenant, who based their religion around a partly misinterpreted and highly mythologized reading of Forerunner history. The Covenant regarded all Forerunner technology to be holy, deriving much of their own technological base from Forerunner artifacts, and most notably believed the Forerunners had ascended to godhood through the firing of the Halos; by repeating the process, the Covenant believed they could follow in the Forerunners' footsteps. United under this promise, the Covenant flourished for over 3,400 years, converting multiple species to its cause before being shattered by a violent civil war.

Origins
The Forerunners existed in a spacefaring status for at least 70,000 years, based on the dating of various sites conclusively identified as being Forerunner in origin. The Forerunners are believed to have held a preeminent status within the Orion Arm (and likely significant portions of the entire Milky Way) for at least twenty millennia, until their activity abruptly ceased in 97,445 BCE in what is now known as the Halo Event. Remnants of their civilization can be found on numerous worlds, including number of entirely artificial worlds of Forerunner origin found throughout the Orion Arm. The neighborhood of the Orion Molecular Cloud Complex appears to have been the center of their activity and the site of their oldest worlds, even as they started migrating along the Orion Arm and the molecular cloud complexes of the Radcliffe Wave fairly early on, eventually establishing colonies throughout the galaxy at the height of their power.

War with the Flood
In the final centuries of their history, the Forerunners came into contact with the parasitic Flood on a desolate world near the edge of the galactic halo. With unprecedented virulence, the Flood spread throughout the Forerunners' Ecumene, leveraging any sentient biomass — Forerunner or otherwise — to fuel its ever-growing armies. Despite their advanced technology, the Forerunners were woefully unprepared for such an enemy, partly due to their inherent reverence for life and unwillingness to adopt harsh containment measures from the start. For around three centuries, the Flood spread throughout the galaxy. Gradually awakening to the severity of the threat, the Forerunners were able to temporarily slow down the Flood's advance by systematically cutting "firebreaks" into their inhabited systems, razing entire biospheres within dozens of light-years to deny the Flood access to biomass.

However, they were only buying time for the Forerunners' ultimate plans to end the Flood threat once and for all. Far outside the galaxy, an installation known as the Ark was created, and within its foundries, an array of seven final weapons was forged: the Halo Array. By radiating a pulse of exotic, superluminal energies, these ring-shaped superweapons would target any life with sufficient complexity to sustain the Flood, thereby ending the Flood threat. Wholly secret to most Forerunners and the Flood, the Ark was accessible only through a handful of slipspace portals, most of them within the boundary of the Jat-Krula sphere — a slipspace interdiction network that protected the Forerunner core worlds. These portals could only be accessed by special vessels known as Keyships.

Championed by the high-ranked Forerunner known as the Master Builder, the Halos were highly controversial due to their inherent contradiction of Forerunner ideals of preserving life. The Librarian in particular objected to the plan in its early stages, arguing that in order to be contemplated, such a plan would have to include the preservation and continuity of living organisms following the rings' firing. This gave rise to the Conservation Measure, a colossal undertaking to index and archive galactic life at the Ark so that it may be reseeded in the event of the Array's firing. However, the Didact, supreme commander of the Forerunner military forces, remained obstinately against the Halos until the very end, arguing that the Flood could be beaten through conventional means.

For centuries, the Forerunner Lifeworkers journeyed beyond the boundary of the Jat-Krula sphere, preserving galactic biodiversity as best they could, even as the Forerunner military was gradually pushed back toward the Ecumene's core worlds. The final blow came when Mendicant Bias, a powerful AI created by the Forerunners to combat the Gravemind, the Flood's controlling intelligence, was instead convinced to join the Flood's cause. Rapidly descending into rampancy, Mendicant Bias assembled the Flood's fleets in a final assault on the Jat-Krula sphere, intent on reaching one of the portals to the Ark and putting an end to its masters once and for all. Before it could do so, however, the Didact had commissioned the construction of another AI: Offensive Bias, designed solely to defeat its fallen brother. However, with Mendicant's conversion it quickly became clear that the war as a whole was lost, and firing the Halo Array was the only remaining option.

As Offensive Bias' fleet waylaid Mendicant Bias at the Line, the Didact prepared to fire the Array. As he did so he remained in contact with his wife, the Librarian, now stranded on a world she had recently discovered and then promptly indexed: Earth. Of the countless worlds she had visited, she was fascinated by the biosphere of this one, and particularly its primitive sapient inhabitants - humans, who she believed may hold the answers to some of the Forerunners' longest-held mysteries. Attesting to the value the Librarian put on Earth and its inhabitants, she commissioned the construction of a portal to the Ark in the East African savanna, which would be buried and not uncovered again until 100,000 years later.

Finally, the Didact fired the Array from the Ark, sterilizing the galaxy of life. Mendicant Bias was defeated mere minutes afterward by Offensive Bias, and the rogue AI's last known remnant was brought to the Ark for study and containment. While galactic life was reseeded, largely by automated means, the Didact and a handful of surviving Forerunners departed on what they called the "Great Journey", seemingly leaving the galaxy once and for all. This is seemingly the origin of the Covenant myth of the Great Journey, which was mistakenly conflated with the firing of the Array itself, likely due to gaps in the records available to the early Reformist San'Shyuum.

Legacy
Since the Forerunners' fall, various younger civilizations have come across the relics they left behind. While the Forerunners once controlled millions of systems, many of them highly built-up with artificial worlds, stations and more, a scant few of them survive to the modern age. It is known with relative certainty that in their war with the Flood, the Forerunners used scorched-earth tactics to deny the Flood access to their technology and even entire populations. Systems doomed to become fodder for the parasite would be systematically sterilized and entire artificial worlds dismantled by nano-viruses introduced into their self-repair systems. In the later stages of the war, the Forerunners began to artificially induce supernovae in populated systems in order to deny the Flood access to them, leaving behind only irradiated rubble. Another factor to explain the relative scarcity of intact Forerunner technology in the present is simple decay: while advanced, even Forerunner technology decays over tens of millennia without a self-replenishing supply of sentinels to repair it, which is the case on the vast majority of sites.

By the time of the rise of the Covenant, other civilizations active in the Orion Arm prior to them — the Jehioi, the Optem, and potentially others — had already stripped many relics clean of useful technologies. Consequently, intact and functioning Forerunner technology is exceedingly rare, especially on a large scale. Particularly in the regions near the Orion Complex, there are worlds with entire Forerunner megalopolises that now lay cold and dead, free of anything but a scant few artifacts. Most examples of Forerunner technology encountered by the Covenant are mundane items found in ruins of what are usually civilian sites and drifting starships or long-abandoned stations; this has not stopped the Covenant from making use of such technologies, however. Intact military technology is rare, but is found at times; the Covenant did discover less than a handful of shield worlds in their history, though only a pair of them were fully and consistently accessible. Another risk on installations of any importance are native defenses, which are at times so aggressive and powerful as to stymie any attempts at incursion.

Prior to the Human-Covenant War, humanity only had circumstantial evidence of the Forerunners; various vague artifacts and a handful of astronomical oddities hinting at ancient megaengineering. A small number of larger discoveries were cordoned off by the Office of Naval Intelligence as black sites over two centuries of interstellar exploration, though there was no consensus whether these findings were the works of one or more civilizations. The UNSC first learned of the Forerunners as a distinct culture through the second-hand knowledge of the Covenant, though it would not be until the final months of the war that the human scientific community was able to start building a more complete picture of the ancient civilization through data from various operations on Forerunner installations.

Spartan John-117's mission records from Halo Installations Alpha and Delta, coupled with data gathered by the AI Cortana, provided enormous amounts of data UNSC scientists would only be able to decrypt over the coming years. During the Battle of the Ark, ONI units at Installation 00 managed to recover various Forerunner items and data logs, including the "Bestiarum", a summary of the known species of the Orion Arm by an archival AI, numerous clerical records and miscellaneous archival data, various logs of Forerunner battles against the Flood, and a number of transmissions between what appear to have been high-profile Forerunner individuals during their war with the Flood. There are even cryptic data strings now suspected to be attempted communiques by a rogue AI. This data would keep UNSC scientists busy over the coming years, forming the basis of humanity's knowledge about the Forerunners.

In later years, some of this data would be corroborated with Covenant scripture since passed to the hands of the Concord of Reconciliation, with curious and at times puzzling correspondences being discovered between the various texts. The Covenant's library of Forerunner records was extensive; though many were lost on High Charity, these were often mere copies of originals kept in the reliquaries they were discovered in, with secondary libraries of data being held in various epistolary-temples throughout the Covenant Sphere. However, the vast majority of this data was fragmentary and far less complete than the records found in the Ark's near-pristine data systems. Translation was another difficulty, as the Forerunners routinely used numerous languages and dialects and most Forerunner sites lacked auto-translator technology. As such, Covenant translations of Forerunner records were often best guesses at best.

Society and culture
Though little is known of the Forerunners themselves, a fair number of individuals have been identified by name or title in surviving records. The Kandonom Codex, for instance, names the Didact, the Librarian and the Master Builder as individuals of note in the Forerunners' final days. Numerous other names are also recorded; these would be ended up codified in the Covenant pantheon (specifically the pluralist doctrines, which emphasized the individual personages of gods) as greater and lesser Forerunner deities.

It is known that the Forerunners had a form of institutionalized caste system in place, forming a set of social, cultural and professional groupings known as rates. Specialization into given professions was further facilitated through biological modification throughout one's life, ritualized as a maturation ceremonies or initiation rites.

The Mantle
A handful of records procured by the UNSC on the Ark have shed some light as to what appears to have been the Forerunners' guiding philosophy. It seems that the Mantle, also called "Guardianship", was the preeminent belief system or ideology in Forerunner society, based around the core belief that it was the Forerunners' moral duty as a culture to hold stewardship over other life. This involved interference in the development of less advanced cultures and species they encountered, incorporating those budding civilizations into the Forerunner Ecumene as protectorates in which their material needs were met by the Forerunners' superior technology. This policy was notably criticized by the Librarian in her final transmissions to the Didact, stating that the Forerunners' belief in the Mantle had artificially stagnated galactic civilization by stifling healthy competition and diversity, instead making species dependent on the Forerunners and powerless against the Flood's onslaught.

The Covenant knew of the Mantle, though they initially believed it to be a physical artifact which granted the Forerunners their supreme power. Upon it becoming clear it was instead a philosophy, it was for a time emphasized as something the Covenant collective should strive towards. However, this was downplayed after they began to discover increasingly critical opinions on the Mantle by individuals of note, most prominently the Librarian. Later, the Mantle held a position in the Covenant faith that could be described as ambiguous at best; some interpretations went so far as to paint it as a facet of Ruination, which allowed corruption and complacency to set in within Forerunner society, and made them vulnerable to the Parasite.

Other Forerunner beliefs remain cryptic. A pair of references suggest some degree of veneration toward a long-passed precursor race; these precursors were believed to have acted as mentors to the Forerunners in their infancy as a culture. Forerunners also appear to have believed that their own race could one day "follow in the footsteps" of these precursors, though the specific mechanics of this remain shrouded in mystery.

Language
At their height, Forerunner languages were numerous. They had the software for individuals to generate and tailor entire synthetic languages to their taste, and learning a new language was as simple as accepting a minor mutation or downloading a software package. These were often designed around specific professions and use cases like highly-specialized tools. They were also a popular form of artistic expression; as well, many guilds, consortia, cliques, and secret societies had their own unique languages for internal communication, usually imprinted on members upon initiation. However, the Forerunners did utilize a standardized archival language so that their databanks could be read by generations that came long after their own.

In addition, the higher-form psychology of their species also influenced their linguistic strains. Specialized or even artistic languages used by mature Forerunners could be highly esoteric, tailored to weave together artful conceptualizations of higher-dimensional mathematics, alien directions of space and time, and individual viewpoints with multiple shifting frames of reference. This sophistication, as well as the vast number of languages they possessed at their height, were the leading cause in the Covenant's difficulty in translating their documents.

Architecture
One of the ways Covenant and later UNSC scientists have been able to trace the development of the Forerunner civilization as well as the various eras therein are differences in architectural styles. These differences are evident between sites from different eras, which likely indicate changing fashions as well as different subgroups of the Forerunner civilization. Even on contemporaneous structures, both the role and importance of those structures determines their specific architecture, with spaces ranging from fairly utilitarian technical facilities to ornamented, cathedral-like spaces.

One enigma surrounding the Forerunners' relics within the galaxy are the stone structures built based on known Forerunner architectonic themes, including the hard trapezoidal angles and similar abstract ornamentation. Such stone ruins are in fact more common overall than the comparatively pristine metallic structures found on key installations such as the Halo rings. A number of Forerunner stone ruins clearly predate their rise to galactic preeminence, which rather naturally suggests they originate in an earlier period of the civilization's history; others are clearly linked with their more recent period, existing hand-in-hand with mainstream Forerunner technology and design methods. However, there are also various ruins that, while they visually appear to correspond to the staples of Forerunner architecture, cannot be conclusively proven as Forerunner in origin. The oft-rudimentary construction techniques used in such structures has led to an interpretation that such ruins could have instead been built by client races seeking to imitate their masters. The discovery of primitive everyday items and other objects around such ruins has corroborated this theory, though some researchers have also argued that these could have been Forerunner populations cut off from the advanced technology of their mainline civilization. Like in any widespread interstellar civilization, technology level within the Forerunner Ecumene may not have been entirely consistent, with some populations enjoying a lower technology level either by choice or unintentional isolation.

A number of Forerunner installations from the later period of their history are equipped with various self-repair systems. Although the specifics vary, such systems consist of nano- or micromachines embedded in the material itself and self-replicating sentinel networks for larger-scale repairs. Even such advanced technology decays over time, however, and still functional self-repair is now rare, mostly being encountered on installations of significant importance such as the Halos and shield worlds. On some installations, the self-repair system have become corrupted over time and turned against the very structures they were meant to maintain, while in a handful of cases, the malicious influence of the Flood has twisted and contorted structures or parts thereof to self-repair into unnatural mockeries of their original forms.

Biology and appearance
Due to the extreme scarcity of intact records and data, the exact anatomy of the Forerunners remains a mystery. Most Covenant sources agree that in their most common biological forms, the Forerunners were upright, four-limbed bipeds with a humanoid body plan, though it is commonly agreed that they could alter their forms at will, either subtly or extensively, to suit different roles, preferences and habitats. According to Covenant doctrine, such transformations demonstrated the Forerunners' divine mastery over mind, body and soul: they could sculpt flesh as a sculptor does stone, each individual being shaped to perfection according to their station. Cross-referencing of the original Forerunner sources has led human scientists to conclude this indicates Forerunners had developed very advanced biosculpting and neural enhancement techniques.

It is known that for much of their lives, Forerunners wore personal body-assist armor, which fulfilled functions ranging from an everyday clothing and fashion item to a comprehensive life-support system and cybernetic mind-machine interface. The armor had enormous cultural and social significance to the extent that no representation of an unarmored Forerunner survives. Also attesting to the integral role of armor in Forerunner culture is the fact the Forerunner word for armor translates directly as "skin", with specific types of armor being variously known as combat skins, platform interface skins, and so on. Likewise, no detailed depiction of a Forerunner face has ever been uncovered, as the few images of Forerunners depict them with what appear to be visors or energy fields obscuring their facial features; it has been theorized that the Forerunners may have had a cultural taboo on showing their faces in public, or simply did not regard them as important. A few abstract or artistic representations seem to suggest the presence of two to four eyes, two nostrils, and a mouth. However, the exact arrangement and proportionality of these varies greatly by source, as do the head shapes; this is attributed to either creative interpretation, extreme ethnic variety, or changing fashions in biological modification throughout different eras.