What Columbus Already Knew : Krulwich Wonders... Many people believe that before Columbus claimed to discover America, most Europeans -- even the learned ones -- thought the Earth was flat.  But in fact, drawings from the 13th century suggest European sailors knew of a round Earth all along.

What Columbus Already Knew

Since we are coming up on Columbus Day, let’s clear up something.

I grew up thinking that before Columbus discovered (or encountered) America, most Europeans -- even the learned ones -- thought the Earth was flat.

Well, check this out:

Proof that the earth is round: a sailor atop the mast of a ship catches sight of land before a sailor on deck. Sacrobosco's The Sphere hide caption

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Sacrobosco's The Sphere

This illustration comes from a treatise called, appropriately, The Sphere. It was composed by an English scholar who lived in the early 1200’s long before Christopher Columbus crossed the ocean.  His name was John of Holywood; his pen name, Sacrobosco.

According Toby Lester, in his new book about maps, Sacrobosco used this picture not just to argue that the world was round but to show that ordinary folks in the 13th century, sailors for example, assumed the Earth was spherical every time they approached a port:

…a lookout at the top of a ship’s mast, Sacrobosco pointed out, always catches sight of land before a lookout standing at the foot of the mast -- 'and there is no other explanation of this thing,' Sacrobosco wrote, 'than the bulge of water.'

The water "bulges" of course, because sailors don’t see a flat line as they look to the horizon but a curved one...the curve of a spherical earth.

Lester goes on to say:

Thanks in large part to the labors of Arab astronomers and mathematicians, ancient Greek proofs of the earth as spherical had survived into the Middle Ages and were circulating in Europe [when Sacrobosco issued The Sphere]…For centuries afterward the work would be taught and studied in schools and universities around Europe. 'If the earth were flat from east to west,' Sacrobosco wrote, 'the stars would rise as soon for Westerners as for Orientals, which is false. Also, if the earth were flat from north to south and vice versa, the stars that were always visible to anyone would continue to be so wherever he went, which is false. But it seems flat to human sight because it is so extensive.'

So they knew.

Toby Lester’s The Fourth Part of the World, (where I found this story) describes the discovery of a particular map: the first one ever to use the name ‘America’. It’s a wonderful tale and it’s a fine introduction to what maps do, how they are made and how people use them to think about the world, themselves and each other.