Find out why we celebrate Columbus as the man who discovered the Americas. (Shown above, a statue of Columbus in Lavagna, Genova, Italy.)

Updated on Oct. 11, at 3:34 p.m. ET

Monday is Columbus Day, time to buy appliances on sale and contemplate other things that have nothing to do with Christopher Columbus. So much of what we say about Columbus is either wholly untrue or greatly exaggerated. Here are a few of the top offenders.

1. Columbus set out to prove the world was round.

If he did, he was about 2,000 years too late. Ancient Greek mathematicians had already proven that the Earth was round, not flat. Pythagoras in the sixth century B.C.E. was one of the originators of the idea. Aristotle in the fourth century B.C.E. provided the physical evidence, such as the shadow of the Earth on the moon and the curvature of the Earth known by all sailors approaching land. And by the third century B.C.E., Eratosthenes determined the Earth's shape and circumference using basic geometry. In the second century C.E., Claudius Ptolemy wrote the "Almagest," the mathematical and astronomical treatise on planetary shapes and motions, describing the spherical Earth. This text was well known throughout educated Europe in Columbus' time. [Related: Earth Is Flat in Many People's Minds]

Columbus, a self-taught man, greatly underestimated the Earth's circumference. He also thought Europe was wider than it actually was and that Japan was farther from the coast of China than it really was. For these reasons, he figured he could reach Asia by going west, a concept that most of educated Europe at the time thought was daft — not because the Earth was flat, but because Columbus' math was so wrong. Columbus, in effect, got lucky by bumping into land that, of course, wasn't Asia.

The Columbus flat-earth myth perhaps originated with Washington Irving's 1828 biography of Columbus; there's no mention of this before that. His crew wasn't nervous about falling off the Earth.

2. Columbus discovered America.

Yes, let's ignore the fact that millions of humans already inhabited this land later to be called the Americas, having discovered it millennia before. And let's ignore that whole Leif Ericson voyage to Greenland and modern-day Canada around 1000 C.M.E. If Columbus discovered America, he himself didn't know. Until his death he claimed to have landed in Asia, even though most navigators knew he didn't. [Top 10 Intrepid Explorers]

What Columbus "discovered" was the Bahamas archipelago and then the island later named Hispaniola, now split into Haiti and the Dominican Republic. On his subsequent voyages he went farther south, to Central and South America. He never got close to what is now called the United States.

So why does the United States celebrate the guy who thought he found a nifty new route to Asia and the lands described by Marco Polo? This is because the early United States was fighting with England, not Spain. John Cabot (a.k.a. Giovanni Caboto, another Italian) "discovered" Newfoundland in England's name around 1497 and paved the way for England's colonization of most of North America. So the American colonialists instead turned to Columbus as their hero, not England's Cabot. Hence we have the capital, Washington, D.C. — that's District of Columbia, not District of Cabot.

3. Columbus introduced syphilis to Europe.

This is hotly debated. Syphilis was presented in pre-Columbus America. Yet syphilis likely existed for millennia in Europe, as well, but simply wasn't well understood. The ancient Greeks describe lesions rather similar to that from syphilis. Perhaps by coincidence, an outbreak of syphilis occurred in Naples in 1494 during a French invasion, just two years after Columbus' return. This sealed the connection.

But aside from descriptions of syphilis-like lesions by Hippocrates, many researchers believe that there was a syphilis outbreak in, of all places, a 13th-century Augustinian friary in the English port of Kingston upon Hull. This coastal city saw a continual influx of sailors from distant lands, and you know what sailors can do. Carbon dating and DNA analysis of bones from the friary support the theory of syphilis being a worldwide disease before Columbus' voyages.

4. Columbus died unknown in poverty.

Columbus wasn't a rich man when he died in Spain at age 54 in 1506. But he wasn't impoverished. He was living comfortably, economically speaking, in an apartment in Valladolid, Crown of Castile, in present-day Spain, albeit in pain from severe arthritis. Columbus had been arrested years prior on accusations of tyranny and brutality toward native peoples of the Americas. But he was released by King Ferdinand after six weeks in prison. He was subsequently denied most of the profits of his discoveries promised to him by Ferdinand and Queen Isabella.

After his death, though, his family sued the royal crown, a famous lawsuit known as the Pleitos colombinos, or Columbian lawsuits, lasting nearly 20 years. Columbus' heirs ultimately secured significant amounts of property and other riches from the crown. Also, most European navigators understood by the end of the 15th century, before his death, that Columbus had discovered islands and a large landmass unknown to them.

5. Columbus did nothing significant.

With all this talk of a hapless Columbus accidentally discovering the New World, as well as the subsequent genocide of native cultures, it is easy to understand the current backlash against Columbus and the national holiday called Columbus Day, celebrated throughout North and South America. This isn't entirely fair.

While Columbus was wrong about most things, he did help establish knowledge about trade winds, namely the lower-latitude easterlies that blow toward the Caribbean and the higher-latitude westerlies that can blow a ship back to Western Europe. Also, while Columbus wasn't the first European to reach the Western Hemisphere, he was the first European to stay. His voyages directly initiated a permanent presence of Europeans in both North and South America.

News of the success of his first voyage spread like wildfire through Europe, setting the stage for an era of European conquest. One can argue whether the conquest was good or bad for humanity: that is, the spread of Christianity, rise of modernism, exploitation and annihilation of native cultures, and so on. But it is difficult to deny Columbus' direct role in quickly and radically changing the world.

Editor's note: This article has been updated to reflect the correct spelling of the name of Giovanni Caboto.

Christopher Wanjek is the author of the books "Bad Medicine" and "Food At Work." His column, Bad Medicine, appears regularly on LiveScience.