They had no cameras. Statues, art, and folklore was how they recorded what they saw and experienced.
To suggest -- as you apparently do here -- that all pre-modern art is purely naturalistically representational is in defiance both of the facts and common sense. I'm game though: what was the moment, according to you, when human beings took the quantum leap and began to /imagine/ things and then draw/paint/sculpt them? It's clearly before Horace, who discusses the dangers of doing so I'd love for you to provide a specific date.
So, maybe I missed your actual rebuttal to my argument about the conventionality of art, because I'm sort of unwilling to believe your "nobody ever imagined anything until modern times" as a serious response, and saying "conventions aren't real and people don't have to understand them to appreciate art" is the intellectual equivalent of saying you're invisible when you can't see yourself -- you might think so, but that doesn't mean it's true.
Okay, then. Your argument /is/ "I believe what I believe and I don't have to justify it". Sophisticated /and/ intellecectually satifying, then!