I didn't find what I was looking for but this is Socrates:
Also I believe that the earth is very vast, and that we who dwell in the region extending from the river Phasis to the Pillars of Heracles inhabit a small portion only about the sea, like ants or frogs about a marsh, and that there are other inhabitants of many other like places; for everywhere on the face of the earth there are hollows of various forms and sizes, into which the water and the mist and the lower air collect. But the true earth is pure and situated in the pure heaven—there are the stars also; and it is the heaven which is commonly spoken of by us as the ether,