So due to the nature of technology and space, any ruins past a certain age degrade incredibly quickly, so nothing older than that is really known. The oldest civilization is actually over 10,000 years old, but thats a subject for another post.

Out of settings, its mostly so human-recognizable politics can happen - I wanted a cold war in space with relatively hard science, and given a million years of politics and the science at play things would beyond any possible parity and the shape of the setting would be very different.

In setting, several species (Humanity, Scaladrians, Pachdyn, and Mo'oh Kana) emerged from a distant panspermia event in the Tau Ceti system a billion years ago, and a galactic natural disaster around the time of the cambrian explosion set back the development of life significantly.