At left are Ptolemy's half-world map from the Canary's to China and Ptolemy's Map of India
In his book, Columbus Then and Now: A Life Reexamined, Miles Davidson writes “Ptolemy’s Geographia became available in manuscript in Europe in 1409 and was first published in 1475, with five more editions up to 1492.” Cristóbal Colón owned the 1478 edition of the Geographia published in Rome. In this way one can establish that Cristóbal Colón, in 1478, knew at least as much about our world as Ptolemy knew 1300 years earlier and the discoverer, himself, informs us of this knowledge several times.
Dear Reader, were you not told that Cristóbal Colón was the first person to understand that the World was round? Reading through Colón’s writings, one can quickly dispel the false statement made by historians that “Cristóbal Colón was the first to realize that the earth was round and that if you sailed west you would reach the east.” Cristóbal Colon tells us clearly during his account of the third voyage that:
I always read that the world, land and water was spherical ... that Ptolemy and all the others wrote ... by lunar eclipses and other evidence ... Ptolemy and the other wise men that wrote of this world believed it was spherical ... Plinio writes that the sea and land make all one sphere.(3)
As is evident, scholars in Ptolemy’s time understood that the world was a sphere and Pytheas of Massillia had already shown that the earth was a sphere five hundred years prior to Ptolemy.
From ancient times, mariners used the North Star or Polaris as a reference to determine their locations at sea and they sailed by degrees. These degrees are a reference to the 360 degrees of a circle and thus to the globe or sphere.
Since 360 degrees is a constant in any circle of the sphere, the only element that changes is the number of miles in each degree as we move away from the Equator to the poles. The largest circle is found at the Equator while the shortest circles are at the poles, (see Figure 1.2.).
Imagine that in the late 15th century the Portuguese experts had calculated the sizeof the earth to within four percent of its true size and yet at the same time a schooled navigator, as clearly Cristóbal Colón was, was incapable of making the same calculation. Cristóbal Colón lived in Portugal and navigated with the Portuguese for King John II, who called him ingenious and industrious.(5) Should we continue pretending that Colón, who utilized the same knowledge and sciences as the Portuguese navigators, would not know how to take these same measurements? Clearly he knew.
This must be the accepted and logical view for anyone who wants to be a realist. To think otherwise would be to keep promoting a fantasy of an ignorant and lost sailor."
(Translation extracted from Colón. La Historia Nunca Contada "Columbus. The Untold Story")