This was before the coming of the Dual, this was the creation time.  

It was before the Shashnimyn were prevalent on the planet.  Similar beings in appearance, they diverged like neanderthals from humans.  Only they were the dominant species, and the Shashnimyn's ancestors still ran from them, simple tribes to an advanced race.

The fossil records still show a path of evolution from early to advanced creatures.  But there are prominent fossils showing that certain individuals were of incredible proportions compared to the rest of the species.  Not just gigantism, but also bones made of crystal and magical tombs that still carry the effigy of these individuals.  They arose as a few powerful godlings which errected a grand civilization.

But this civilization collapsed.  They over-consumed and did not live in harmony with the planet.  Their springs ran dry, their forests and fields turned to deserts, their mines went empty and their magical energy powerplants imploded upon themselves.

Remnants of the First Peoples

When adventuring in the wilderness, you can seek to find lost artifacts and buildings. there are many villages founded on the remains of past cities. there is flux where the jungle or desert reclaims the buildings, only to be found or uncovered.