So the whole Roman empire is one civ - we're going with that? Or have we decided? I for one am convinced that a contiguous Roman empire could not last until 1500 (which is probably when China would discover the Aztecs, as mentioned). The Native American civ is a cool idea (mildly implausible though, considering the massive diversity of language and culture in any substantial area), but if we have a pre-1600 start whether or not it would spawn would depend on in-game events, rather than a fixed date. (If the Aztecs ignored the rest of North America, their spawn would be completely implausible.) And I agree with Kairob on the Aborigines - they had exposure to agriculture (well, at least some did, by trading with people on islands south of New Guinea) and expressly chose not to adopt it.