The accounts describe them as spreading life throughout the galaxy, but they were destroyed in a cataclysm some 500,000 years ago. However, there is no reason to think that their evidence was particularly compelling.
Some popular works have dubbed these the ``Builders'', but the evidence suggests a different story. On several worlds, studies suggest that preexisting ecosystems were destroyed in the process of terraforming. Thus, rather than spreading life, this civilization destroyed other life in favor of a more homogenous array.
Whether or not the ``Cataclysm'' was true, no evidence of interstellar technological activity (terraforming or otherwise) has been found for the period from 500,000 years ago to approximately 100,000 years ago.
The Preservers are known primarily by their efforts to proliferate and guide the development of many primitive bipedal species. We have some artifacts from them - tools from their efforts, but we still have no view into their civilization itself: their homes or personal effects.
What evidence we do have is rather suspect, since the purpose of many of their efforts was to influence the development of culture. Thus, what we see is mostly what they wanted us to see: pre-planned images which may well have been part of their plan (whatever that may be). Until more primary sources of information can be found, any conclusions must be quite speculative.
The apparent ``Great Project'' of the Preservers was to spread selected cultures to other planets where they could develop independently of foreign influences. Thus, throughout our corner of the galaxy we find races with near-identical genetics from different planets. The suffix '-oid' is usually used to refer to such related races (i.e. the humanoid Alpha-Centaurans, or the Klingonoid civilization of Axanar).
The Great Project started perhaps 14000 years ago, and has continued until at least 3000 or even 1000 years ago. It took on many forms, including terraforming of planets' ecospheres and the genetic manipulation of transplanted peoples. In some cases, the Preservers used mechanics to create an artificial natural or cultural environment. The ``paradise worlds'' of Gamma Trianguli and Eta 131 are the most well-known examples, but they are less than ideal in many ways for archeological study.
The tools used for these projects are among our best evidence for the nature of the Preservers themselves. While their external appearances are for show, the microstructure and interior design has led to a number of suppositions (to be described in a later work).
Given the nature of the Preservers, it is not surprising that many wild theories are thrown about. While it is easy to dismiss such claims, it is important not to ignore all possibilities.
Given the past behavior of the Preservers, it is certainly possible that they are still present in this area of the galaxy. They have consistently kept themselves hidden from less advanced races for millenia. It would be extreme arrogance to imagine that we could detect a race that much more advanced than ourselves.
A reference list of some Preserver works:
- Intervention as the the ``Sky Fathers'' of Cygnan culture.
- Humanoid cultures: Alpha-Centauri, Argelius, ...
- Paradise worlds: Gamma Trianguli(`The Apple') and Eta 131
(`The Paradise Syndrome')
Questionable Suppositions:
- Influence of early Greek culture on Terra (`Who Mourns...')
- Influence of later Terran culture (`Assignment: Earth')
Clearly, Rigel was the center for an immensely powerful ...
The ``Old Rigellians''
Clearly more diplomatic work could be of immense usefulness in this field.
The Camans were a highly philosophical people, whose technology waxed and waned according to fashion.
...
The unique feature of the Camus civilization is their thought-based electronic technology. They were able to holographically store memories, meld minds, and many other operations through advanced neurochemical connections. [...]
The peak of the Empire was around Y-500 or so.
After Y-400, the King's imperialism waned.
They disappeared around Y-230 or so. In their decline, the Kings abandoned and destroyed many of their stations, and whole populations transported off to parts unknown. Sensing weakness, the Klingons revolted, capturing a number of ships and bases from within.