I don't really think 'we-know' or have any idea, except from what we have 'read-or-heard' about from those who came before us.
Then, from this, we must ask ourselves, "Have we actually understood?"
And,,, not far from what Sitchin has suggested,,, have we misunderstood what we think is correct???
Everything we 'think-we-know' could well be far from the truth...
Did ancient-Egypt actually build the pyramids or did they simply "discover-them" when they first arrived in that area???
Some of "orthodoxy" actually think the Egyptians built them.
But, today's technology doesn't actually have the capability of doing the same task,,, as best I can find.
Perhaps we simply "do not know"...