A Round Earth.

Among the great myths concerning the age of exploration, perhaps none is more powerful and durable than the widespread notion that Christopher Columbus proved to a disbelieving Europe that the earth was in fact round and spherical, not flat. In reality educated Europeans had understood that the earth was spherical for at least two millennia before Columbus's 1492 voyage. As early as 500 B.C the students of the mathematician Pythagoras were already speaking of the earth's spherical shape. Evidence for the earth's sphericity came from a variety of observations. The ancients noticed, for example, that the hull of a ship sailing away from an observer disappeared before the tip of the mast, suggesting that the earth's shape was curved. Similarly the ancients noted that the circular shadow cast by the earth on the surface...