The History of [insert cool world-name here]
In the distant past at the dawn of the world, the Gods and Titans (Primordials) battled for control of reality, with the Gods ultimately winning with the help of mortals.
The mortals of ages past formed a civilization of immense power (creating various cool artifacts and ruins), but for some mysterious reason their civilization has vanished.
A great (and vaguely Roman?) republic existed in the past but fell apart generations ago as a result of infighting? Perhaps called the Cerilian Empire or some other cool and slightly Roman name?