yep, million dollar question.
They could represent an ancient SETI search, they could be designed to communicate with the gods of the time, they could be real life depictions of a visit from elsewhere -- who really knows ?
We have lost 99 % of all species to ever have lived on earth, we have probably lost a very large percentage of technologies ever developed.
It is possible that todays technology could be applied to certain ones from the past to create something very powerful.
