When did the notion of a flat earth become pop and why? A hypothesis wot comes to mind is that it aids in maintaining the status quo since exploration could result in "falling off the edge". Clearly, a curvature of earth would have been common knowledge to any seafaring folks at least. Large ships do not just appear to become smaller with distance, but gradually disappear from the bottom up. I think it it is important to distinguish betwixt knowledge and superstition. The latter may persist even in the face of the former's long standing. As inferred by the article, the knowledge was documented at least two millennia before the earth was circumnavigated, yet even at that time ignorance persisted amongst some and was in the interest of others to maintain.