"The new geography was summed up by Eratosthenes (ca. 275-200 B.C.),
 who worked at Alexandria.  Using observations from a variety of sources,
 he reached many important conclusions.  He calculated the circumference
 of the earth as 24,662 miles, about 200 less than the actual figure."
 ...
"Meanwhile, Spain was sending her mariners westward, for by the late
 fifteenth century most educated people in Western Europe assumed that
 the earth was round, although they greatly underestimated its size."

    _A Short History of Western Civilization_, Harrison and Sullivan