He surely instructed the sailors in his belief that the distance from the Canaries to Cipango was only 2,400 nautical miles, and—fortunately for them—the islands lay at virtually the same latitude (as in fact they nearly do); all the ships had to do was hold a course directly west. If the fleet were to come upon unknown islands on the way to Asia, they would be useful to reprovision before bringing in rewards of discovery.

His years of studying both ancient and contemporary geographers and travelers (including Marco Polo who wrote his account while incarcerated in, of all places, Genoa) convinced Columbus that Asia was a land stretching so far north and south that no westering sailor could miss it if his nerve and will did not fail him; nor, so he believed, was distance really much of a concern since the Atlantic was narrower than most learned men of his time assumed. In the years prior to departing, when Columbus was trying to convince various royal scientific committees about the feasibility of his voyage, the major disagreement wasn’t, as is popularly supposed, whether the world was flat, but rather how wide the Ocean Sea was. Many of the scholars opposing Columbus were closer to the truth than he, but as a man of medieval mind, he worked at things deductively: he knew where he wanted to go both in logic and on the sea, and he searched out views to support his own. We shall see this propensity again. The many, many annotations in three of his books of cosmology and geography reveal his geographical conceptions and his absolute stubbornness against admitting any evidence that might overturn his deep urge to find a westward sea route to the riches of the Indies. In his copy of Pierre d’Ailly’s Imago Mundi (Image of the World), Columbus noted sentences like this: “Between the end of Spain and the beginning of India is no great width,” and “Water runs from pole to pole between the end of Spain and the beginning of India,” and “This [Ocean] Sea is navigable in a few days with a fair wind.”

Nevertheless, knowing his men’s fear of sailing past a point of return that would doom them, Columbus cautiously, wisely, kept two figures for the distance the ships covered each day: one he believed accurate and the other a deliberate underestimation to report to the crew. The lower figure also served to keep expectations down and increase their tolerance of long days with no signs of landfall. Some of them surely had heard that to reach Asia by a westerly sea route would require a fleet capable of being outfitted for a three-year round trip; and since it seemed unlikely there could be any undiscovered lands between Europe and Asia for reprovisioning vessels, the crew believed men on such a voyage would perish at sea. As a discoverer, Columbus was a lucky man—even the geographical errors he made often worked to advance his goal. His achievements were the result of many things: incredible determination, fearlessness, capital abilities as a navigator and leader. But none was more important than his capacity to persuade Ferdinand and Isabella, especially the Queen, of the possibility of his correct notions. Had the American continents not been in the way, his sailors likely would have died before reaching Japan, a land almost five times farther from Spain than he calculated.

Of all the notations in his various books, one from Seneca, the Spanish-Roman philosopher and playwright, is most revealing: “An age will come after many years when the Ocean will loose the chains of things, and a huge land lie revealed; when Tiphys will disclose new worlds and Thule [Iceland] no more be the ultimate.” Again, an error encouraged Columbus: Tiphys is the pilot of Jason’s ship of legend, Argo; but the name Seneca actually wrote was Tethys, a sea nymph. The irony is that the Columbian version of the prophecy, whether miscopied or not, more accurately describes what he truly found than what he meant to find.