The Archive is a pseudo-clerical order of librarians, historians, scientists, scribes, priests, monks and more, based out of the Imperial City on Tarsis.
Combine all the intrigues of the 15th-century Vatican and all the disorganized bureaucracy of a library the size of small city, and the general idea of the Archive's day to day functioning is formed. Thousands of years of information has piled up in an order dedicated to the preservation of knowledge. Most of it, gathered on the intent to save it, has been lost anyway, because no one knows where anyone put it in bygone centuries.
Originally, the Archive was just supposed to be a repository of knowledge. For most of the Coalition's history, it has done exactly that, formerly assisted by the Zaian and sometimes other races. In fact, its found, High Chronicler Atheran, was a Zaian himself. It took an immortal to wage such an effort in the early days.
Once space flight was recovered, the Archive set about finding the remnants of the cataclysm. There were entire planets where the monstrous constructs birthed from the beacon networks still reigned free. In some cases, survivors held out, and the newly-formed Imperial Navy was sent in to rescue them; and even liberate the planet when it was possible. But for most discoveries, the cataclysm's constructs had annihilated anything alive and resigned themselves to lurking in the darkness, waiting to ambush anyone dumb enough to step foot onto their domain. As they proved resilient to destruction, these planets were declared off-limits, and abandoned forever. The Archive still keeps an eye on them, and searches for others near or even within Coalition territory, while making sure no one ever gets to that point of advancement again.
Every now and then, the Archive gets bold and send expeditions to the ancient computer banks that stored everything the Old Coalition knew. Usually, these come back empty-handed, or never come back at all, but sometimes they do find something. But if what they recover isn't infected with malevolent contagion, then they still have to deal with the fact they do not understand how or why it operates. The Archive keeps many artifacts in their citadel, things that are too risky to activate or things they don't even know how to turn on.
Aside from watching out for forbidden technology and occasionally going to find some for itself, the Archive also records everything it can, for its vast stockpiles of data. Sometimes this information becomes useful later, but most of the time, it just gathers and is never touched again. But because the Cataclysm destroyed almost all knowledge of how things used to be and essentially screwed over everyone, the Archive isn't keen on letting anything go. In addition to the central citadel on Tarsis, there are Archive repositories (often performing a similar function for another partner race) on such planets as Othaen, Thyrenda, and Digondar. Just in case.
After Atheran died against in battle against nightmare constructs, it rapidly strayed from its intended purpose. Within a few hundred years, the Archive had gone from a supposedly secular organization with an unofficial ministerial tone, to outright agents of the Zaian faith, at home and abroad. They merged their theological quest with their academic and exploratory one, and soon a military quest as well, given how most guilds and other orders have had to fend for themselves from time to time. In Earth terms, the Archive has become akin to a scholarly crusader order. The Chancellor has held the reins of power ever since, an arrangement the Zaian are quite fine with. As long as everyone keeps in line with their ideals, they see no reason to change anything. However, plots and corruption have grown in the once-venerable institution. There are even rumors that the current Chancellor furthers such illicit activity...
The Citadel of the Archive
The Archive's citadel tops out at 1300 meters, or about 4265 feet, roughly three times the height of Earth's Empire State Building, and many times wider at its base. The structure was built into the side of one of the mountains bordering the valley the Imperial City it lies in. It is unclear who built the citadel; either the work of lost arts from before the cataclysm, or the work of Zaian techno-sorcery in the misty years of the cataclysm itself. If it is the former, the original purpose of the building has long since been forgotten; if it is the latter, then the Archive has always been there. As typical for any ancient building, the Archive's citadel is riddled with secrets. Hidden passages, halls, and rooms lurk behind any wall, or sometimes in plain sight; while parts of the structure that are supposed to be there are simply not accessible. These secret ways have been discovered by many a Chronicler over the centuries, but they are seldom shared. They can be powerful instruments in the internal politics of the Archive, where intrigue has taken a deep root.
The crown of the citadel is the final iteration of the tower structure, called the Reliquary. It is unknown at what date it came to be known by this name, but it was definitely after the death of the High Chronicler Atheran. On the highest level of the Reliquary, above even the Chancellor, is the Apse of Atheran, in which the body of the Zaian himself is kept, in the same ornate armor he died in. Below that is the abode of the Chancellor, below that the abodes of the Arch-Chroniclers and their Conclave hall. The rest of the tower is given over to holding treasured artifacts, books, scrolls, and scraps of uncorrupted digital files recovered from ancient computer banks. The secret plans to plasma weapons, etherspace engines, and more are also stowed away here, in hidden halls and supposedly sealed-off rooms.
The Upper Archive
Below the sanctum of the Reliquary is the Upper Archive, where other valuable records are kept. Tithe returns, centennial census records, fleet actions, recovered data on Old Coalition equipment, star-charts, etherspace current charts, and more can all be found. Vast stacks of books can go on for floors and floors, representing just one fragment of information collected in the vast history of the Coalition. This is true of all levels of the Archive, but especially here, which houses almost entirely books and charts. The citadel's reputation of being a mass store of dust collecting surfaces is mostly due to the Upper Archive, as it is not as busily frequented as the Lower Archive and Reliquary are. Also of note are the quarters for the Chroniclers of middle-rank, which are located in this section of the citadel.
The Lower Archive
If it could be said that the Reliquary holds the brain of the Archive, than the Lower levels are its heart. It is devoted to recent records of all importance, or lack thereof; to hosting the Chroniclers; to the chambers of the scribes; and to service of the Faith. It also hosts one of the few public libraries in the Coalition. Everything that has been recorded in the last thousand years is somewhere in the Lower Archive, if it isn't important enough to be in the Upper. Anything from a sector's grain production last fall to trade conditions in the Kingdom of Thyrenda six hundred and twelve years ago, it is here... Somewhere.
The scribes of Tarsis also make their work here, copying out decaying books onto fresh pages, a never ending battle against entropy. Some few even work to produce new books. A great cathedral has been attached to the Archive as well, where the faithful come to venerate the Great Lord whose living will is embodied in their Emperor and whose word is carried by the Zaian. Where there aren't towers of records, halls of scribes, or places of worship, there are the dormitories where the lesser Chroniclers live. Most are one-person two-room nooks with just enough to provide the necessities of life, though it's not uncommon for Chroniclers to share rooms for access to working heaters in the winter. Some Chroniclers don't even bother with rooms, they just sleep wherever they can avoid being disturbed. This can mean secret chambers and halls, overlooked and deserted areas, or even unorthodox residences like air vent shafts and unused shelves on massive bookcases. Free meals are provided on the ground floor, but crafty Chroniclers with the spirit of free enterprise and the skill to cook have opened up their own food services, for a price.
The Deep Archive
This is the part of the Archive most people will avoid. It might be a remnant of an older structure, which the citadel was built over. How deep it goes and how far it extends, no one is really sure. High Chronicler Atheran's expeditions in this place revealed that it was at least as deep as the Archive was tall; but horizontally, it varied greatly. He found that there were scores of tunnels branching off from it, ones he believed would eventually lead to the subterranean computer banks. Unfortunately, the underworld of Tarsis has become a nightmare that none dare enter. Atheran's great worry was that these tunnels leading into the Deep Archive were not sealed in any way, and he could not do the job himself without the proper equipment.
All the trivial records of millennia gone by have been transferred into various parts of the Deep Archive, usually within the first few hundred feet. Dangerous artifacts brought back by expeditions are also locked away down here, much deeper than any record. Only the fact they are down here is noted, their locations are deliberately obscured and lost so no one can ever find them in the vast underground maze. It is forbidden for anyone to venture lower than twenty stories below ground alone, and it is all but completely forbidden for anyone to venture lower than seventy stories no matter the circumstance. Only the Chancellor may authorize access that deep, and a contingent of the the Archive's own retainers must be taken along. Perhaps Atheran's fear was right, and the horrors of the Tarsin underworld have broken through whatever his protective measures were.