To say something, concerning humankind, “is eternal” is a conceit. But until it is proven as such let’s assume otherwise.
It is fair to speculate that every notable society pondered its eternality or its ending. Endings of this sort may seem rather debatable given that every generation of a society experiences its own time as a gradual unfolding of events; rarely, if ever, an ending and a new beginning.
The cumulative impact of these events is rarely clear at the time, if ever. In hindsight, the turning point toward a society’s failure to endure can be better seen even if not clearly. It’s rarely a single, major event but, rather, a series of minor ones that begin and perpetuate a deterioration as a cumulative affect.
It is interesting to read contemporaneous accounts of events that happened in the past. Some of these events might be all but forgotten now, except by historians or as blithe footnotes in the collective consciousness. But, at that time, the events may have seemed monumental. It is equally interesting to note that just the opposite is often as true; seemingly minor events take on historical importance or rememberance only long after the event has occured.
History is, in many ways, remembered eternally, though often in the unanticipated.