Archaic Oikumene

It's commonly accepted that most of the galaxy's sophonts are either descendants or creations of humanity who came into being on the fabled world of Earth. The location of this ur-world of the humanoid phyle is lost. 

The original civilization of humanity collapsed (perhaps multiple times) or perhaps it ascended. Whether the end was glorious or tragic, the true history of these times is only fragmented legend.

The Archaics rose with the aid of knowledge recovered from the ruins of the past. They built floating, crystalline cities, constructed the hyperspace travel network (even connecting the noospheres of their core worlds with superluminal relays), and engaged in planetary-scale engineering. Theirs was an age when a noble might rule an entire world populated by her clones and sophont warships fought grand battles for audiences in telepresence.

Something happened — something called the Great Collapse. Galactic civilization fractured into individual worlds, and some of those worlds slid back into savagery. Much of the available historical record of this time appears to have been deliberately altered to obscure events. The time separating the Great Collapse from the present isn’t entirely clear, but may it be 1,000 standard years or more.

The salvager holy grail would be one of the twelve great battleships of the Archaic Oikumene, vessels the size of cities with sophont minds. 

Some of these great ships (like Terrible Swift Sword and Leviathan Smiles) are known to have been destroyed. Others (like Achilles’ Last Stand, Fearful Symmetry, and Conspiracy of Ravens) have disappeared completely from history, possibly re-structuring themselves into vessels of different types.

PSI PHENOMENA moved fully from the realm of fringe belief to exploitable technology during the Archaic Oikumene. The hyperspace network is the most prominent example, but not the only one; other psionic devices exist.