DY: This has always been an issue that troubled me. I know what the Meforshim (all quoting Rashi, really) say. However, they never saw such a statue.
It seems inconceivable (and honestly, a bit insulting) to me to have the Tannaim talking about a theoretical yet nonexistent statue when there was a statue that meets the Gemara’s Lashon perfectly that would have been in just about every city. Almost all of Maseches Avodah Zarah is in context of what the Goyim did. Why on earth would they not be referring to Zeus (who is almost always depicted with a staff and a bird) and Atlas? It seems foolish to make the Mishnah talking about the theoretical when the practical is obvious and right there. Rashi was unaware of what their idols looked like. We are aware and it fits the Gemara perfectly.
HaLeiVi: It was a Machlokes among the philosopher’s. Round earth began to spread after Aristotle “Paskened” that way. But most before him held it was like a disc in the ocean.