Those civilizations which do not, upon comprehending the blasphemies inherent to such technologies, extinguish themselves have, apparently without exception, "Passed" to the "Beyond, an existence, we must assume, in some other reality incomprehensible to us.
It is sometimes said that the "H" of H-level technology stands for "Ha ha ha hahaha!"
Level I stands for Inherently Imperial; possession of a tech level I artifact without special leave by a member of the Imperial Family is treason. Level H and even level G items may also frequently confiscated, but may not be inherently illegal. It depends upon the effects of the item in question and the owner's standing; a license is recommended.
Imperial scientists and engineers of level H and I are kept secured, as they are inherently insane. They actually work less on trying to comprehend the Ancients' artifacts than simply trying to figure out how to use them, or their cannibalized parts.
The artifacts of the Ancients are often unfathomable. Indeed, the definition of an "Ancients" artifact, as opposed to simply an item of high technology and great antiquity, is its incomprehensibility.
The Empire makes extensive use of recovered artifacts of the ancient, incredibly powerful, and (supposedly) long gone Ancients. These artifacts, or their cannibalized parts, are tools that, even in their present state of decay are yet far more powerful than any contemporary technology. The technology level of the Ancients was far above any now under development.
Most Level I artifacts are used as "black boxes" without any dangerous prying.
It is likely a good thing that we have discovered precious few of the Ancients' personal weapons, and fewer still major armaments. What we have are their every-day gadgets and toys. That we have adapted so many of these to military use says more about our civilization than it does about them.
Creation by - and for - synthetic intelligence may explain why some ring-worlds or sun-drums and other vast artifacts do not have or did not have their inner surfaces "landscaped" for organics, or have anything like a standard gravity. Only when the synthetic intelligence is, for one reason or another, gone do organics colonize and modify.
Happily, many others were built with organic habitation in mind, or have already been so modified by other Ancients.
Many of the Ancients, including the Ancient Inquestors, developed AI and loosed these synthetics upon the multiverse.
This shows that many of the Ancients were not enlightened as to the basic, inherent obligation of civilization to accompany the spread organic life throughout the multiverse with the suppression of synthetic life; they did not know the Great War. Some may, in fact, have been given the Trojan Horse of H level technology in a plot by some devious synthetic intelligence.
It is a blessed miracle that so few of the Ancients' AI machines (such as their automated seeder ships) have not turned against us.
SEE The Imperial Inquest for more data on the Inquest.
The most recent of the Ancients civilizations was that of the Inquest of the Ancients, so-called to differentiate it from our contemporary Imperial Inquest.
The civilization of the Ancient Inquestors seems to have "Gone Beyond" only a dozen millennia before the Empires which woke to the necessity of the Harmony, woke to the necessity of bringing all organic life into harmony. The extreme decadence of Ancient Inquestor remains is a bit of a distortion; the artifacts from the end of their civilization's inhabitation of mundane universes reflects the seeming-madness just preceding their Passing on to the incomprehensible Beyond.
The Inquestor civilization did not, in all probability, last as many millenia as The Harmony has before those Ancients Passed. Researchers believe that the Ancient Inquestors, the very civilization known for having extinguished worlds for the heresy of Utopia, was also the most prolific in launching Seeder ships to bring life to new worlds.
SEE Lovecraftian Horrors in the Multiverse
There are Lovecraftian horrors, alien beyond mundane monstrosity,encountered by those most unlucky, where the vile beings have slipped from their cryptonic other-realms into our mundane universes. These beings are truly alien; they could not belong in any sane universe such as we mere mortals could comprehend. It is horrific enough to consider that there must exist universes, or rather dimensions stranger still, where such blasphemies do indeed belong, without our being forced to the mind-shattering realization that they may, upon apocalyptic occasion, be able to inflict a shadow-made-substantive of their inconceivably bizarre real selves on our all-too-vulnerable mundane universes.
Any artifacts suggesting that such horrors, or even lesser monsters merely tainted by their shadows, may have inhabited some mortal worlds, are better destroyed than understood.
Some have seen glimpses of their impossible reality during inter-dimensional travel. Such ravaged souls are kept safely confined, if death has not been merciful enough to spare them their visions.