The possibility that Asia could be reached
by sailing west was accepted by some geogra-
phers of the era, but none of the European
maritime powers were willing to support such a
risky and potentially dangerous enterprise. No
one knows how Columbus became obsessed
with his belief that such a voyage was possible.
By the time he was commanding ships, he had
plenty of practical experience at sea and access
to the charts of his late father-in-law
Bartholomew Perestrello, a seasoned navigator.
Columbus corresponded directly with Paulo
Toscanelli, a respected Florentine scholar who
believed that Asia could be reached by sailing
west. Toscanelli had provided the king of Portu-
gal with a world map upon which an ocean
separated the coasts of Europe and Asia. The
map, however, depicted nothing but open sea
where the Americas lie and greatly underesti-
mated the distance between the Canary Islands
and Japan, which Toscanelli computed to be
only 3,000 nautical miles, far less than the
actual 10,600-mile distance.
Columbus’s own calculations owed less to
Toscanelli than to French cardinal Pierre
d’Ailly, author of a geographical work called
Imago Mundi (Image of the world), which
stated with certainty that Spain and India
were within sailing distance of each other. In
d’Ailly’s treatise Columbus found the calcula-
tions of the ninth-centuryArab astronomer
Al-Farghani, also called Alfraganus. Columbus
misinterpreted Al-Farghani’s calculation that
each degree of latitude at the equator was
approximately 66 nautical miles (today the
figure is computed to be 60 miles). Thinking
the figure to be only 45 miles per degree,
Columbus calculated the distance between
Japan and Europe to be a mere 2,400 nautical
miles. Although this was a significant distance
to mariners of the era, Columbus’s belief that
he would encounter islands along the way
made it seem worth the risk.
All 15th-century geographers underesti-
mated the circumference of the Earth. Colum-
bus’s faulty calculations determined that the
Earth was only 25 percent of its actual size.
Had he not been so wrong, believing the globe
to be so much smaller than it actually is, it is
unlikely he could have convinced anyone to
fund his voyage.SEARCHING FOR A PATRON
Columbus endured ridicule and waited for
years before he found a sponsor for his firstThe Four Voyages of Columbus B 25
Sebastiano del Piombo completed this portrait,
believed to be of Columbus in 1519, 14 years after
the explorer’s death. (Library of Congress, Prints and
Photographs Division [LC-USZ62-103980])