'Histories', as a term we understand today, the forensic records of events in ordinary time, came much, much later.
Myths are the histories we told of the time before time.
By "once upon a time" we should immediately understood not a time in the sense of tempus or chronos, but rather in that “age” (aevum, aion) that lies in the interval between our time and eternity.
In Genesis 2, for example, YHWH Elohim "took the man, and put him into the garden of Eden to dress it and to keep it." (Genesis 2:16)
It was the Gods who taught us to speak of ourselves as placed within nature but also somehow set apart from it.
Myths recall the time, that once long ago existed, when anthropomorphic deities and theomorphic human beings walked, as it were, and talked. In those tales, where the Gods told us about our origins, taught us to think for ourselves, and offered salutary warnings about the calamities that lie in wait, that even they could not avoid ... those myths shape who and what we are, even today.
We cannot escape them. They are our Dreamtime. It's no coincidence that the Greek Myths encompass the archetypes of human psychologies.
We cannot escape the fact we are narrative creatures, and the most powerful and natural narrative idiom is the myth – it shapes us entirely.
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And they are true, in their own sense, and real, in a way our modern histories are not.
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Myth is the most real, the most true and the most beautiful narrative form.