Wikipedia has proved useful in this regard- it appears that the notion of Columbus challenging the idea of a flat earth was likely first made by Washington Irving. Somehow, I hadn't remembered this from when I read "Lies my Teacher Told Me". It would be fascinating to know if Europeans, as a whole, don't have this idea of a classical flat earth, but in some regards, it would seem that this is an entirely american fiction.
Conceptually, the middle ages and the dark age are greatly muddied in my head. The early period, the "dark age", and the arrival of the plague or "black death" are antipodean, unlike my conception from what I have been taught: that the middle ages arose not only from political upheaval after Roman schism, but also from a utter decimation of the population by plague. In fact, many charts I have seen of population of the world show a dramatic plunge in world population due to the plague, when in fact it may only have been a local phenomenon in Europe, and a consequence of the transition to city and military concentration of population which are post-middle age and nascent reinassance activities. Later incidences of plagues such as smallpox in the American continent, as popularized in "Guns, Germs and Steel" by Jared Diamond, which likely date to the 17th century and later, don't generally enter the depictions of population.
Also, questioning this would be any evidence as to the Arabic and Chinese civilizations' population might be. In fact, the era conceptually defined as the middle ages did not exist from the vantage point of the east, since the height of the Tang dynasty is dated within the dark age. Populations and loci of civilization have been migratory for ages much beyond that of curently recorded civilization. There are many ancient, highly populous, and almost completely erased civilizations such as those near Myanmar and in central America, and as a human society loses its locus, the evidence of its existence begins to disappear, but that is not synonymous with genocide or decimation- old people die, and their children move away: but that does not mean that the population is "lost", merely transformed. I believe we see human society as impermanent, and therefore concepts as abiogenesis take hold because we would rather believe that life arises spontaneously from the immortal than to see all of existence as a changing, impermanent system.
As a strict concept of western history, the so-called middle ages seems to be a commentary on modernism- that the rise of humanism and analytical science in Europe represented a new age through which imperialism and capitalism could be given reign and permit the economic and political expansion of Europe beyond previous familal and national borders. If I understand correctly, this can be traced forward to the philosophy of Heidegger and Arendt, who talk about the fundamental "homelessness" of modernism, where technology separates human intentionality from the world which sustains human existence. We need to see a difference between the natural mode, where human endeavour is shaped and limited by greater natural forces, and the technological mode, where human endeavor shapes the natural world.
In reality, the concept of a flat earth probably should be replaced by the concept of a uniform earth as an object of study. The difference between the modern era and prior civilization has nothing to do with enlightenment, but the shift in thinking away from a strict uniformitarianism (whereby the action of people is limited and the earth underneath is unchanging and immortal). It does not seem sensible from a human perspective that the earth moves- we understand from a naive standpoint only a static frame of reference relative to ourselves. We have to explain, then, why people change and die- it is because that which is human and worldly is somehow different from the eternal, the apparently unchanging solidity of the earth below and the unchanging ether of the sky above.
Unlike a flat earth, which is only supportable by being selective about citing sources, nearly all classical sources have some form of platonic "form" embodied within it- an appeal to a dualism between what is eternal and what is not. As the temporal world becomes perceptively less eternal, classic thought is best represented as transmuting the concept of the eternal from an animistic one to a supernatural one, of either "forms" or an immortal, incorporeal "god". (Before modernism, the concept of "no god", as far as I can tell, did not exist- to declare such a thing was to be perceived as insane, or simply heretical- "no god" meant "something other than our god", emphasis on something, or agnosticism.) In this light, the modern era may still not have taken hold, despite science. We don't see environmental change as something natural because it is caused by human action- environments changing over time is a simple truism, but rather we invoke a dualism between the corrupt material of human existence, and the incorruptible natural universe. This does not mean that a separate value judgement can't be made- we can decide how we wish to interact with a changing environment and shape our actions accordingly. However, we cannot appeal to any eternal concept to determine the proper or ethical mode of action. Modernism is something which still hasn't happened, because we have not fully worked out what a post-authoritarian social existence will look like. It may even be plausible that such a thing cannot occur (and is why I need to read up on Leo Strauss).
Phenomenology is definitely a start- describe things the way they are, not how you theorize them to be. But, while all the pieces are beginning to fall into place, I wonder if it isn't like pre-1900 physics: you can have all the pieces, like Laplace and Maxwell, and still not have quantum mechanics to hand.