We don't have to wonder, because he wrote it down. Ptolemy estimated that the continents of Europe and Asia collectively spanned 180 lines of longitude, leavin

We don't have to wonder, because he wrote it down. Ptolemy estimated that the continents of Europe and Asia collectively spanned 180 lines of longitude, leaving 180 to travel by sea. Most contemporary scholars believed this too. In actuality, the continents span about 130 from China to Spain, leaving 230 that would need to be travelled by sea. The best sources available to Columbus were wrong, and the other available sources typically erred on the ocean being too small. Few, if any, people thought Europe and Asia spanned less lines of longitude than estimated by Ptolemy. Additionally, he read that each line of longitude spanned 56 2/3 miles at the equator. Unfortunately, his source was quoting Arabic miles, but Columbus was only familiar with Roman miles, which are shorter. He didn't believe that he discovered something the scholars of the day didn't. The fragmentation of the Mongol Empire meant that overland trade was growing more expensive, meanwhile nautical technology and seamanship was rapidly advancing. It would have been impossible to have made Columbus' planned (as he understood it) sea voyage in, say 1300. But now, the overland route wasn't well run, and the caravels used by Columbus were much better suited to ocean travel. If Columbus hadn't done it, the economic necessity of the rising price of goods and dropping costs of sea travel would have resulted in someone else doing the same thing. Some people say he was a unique visionary, other people say he was dumb and lucky. Neither were true. He did his research and came to the natural (if wrong) conclusion. (he was lucky though) https://en.wikipedia.org/wiki/Christopher_Columbus#Geographical_considerations https://en.wikipedia.org/wiki/Christopher_Columbus#Geographi...