How was it that a German priest writing in Latin and living in a French city far from the coast became the first person to tell the world that a vast ocean lay to the west of the American continents?

That is one of the bigger mysteries in the history of the Renaissance.

But it is not the only one involving Martin Waldseemueller, a map-making cleric whose own story is sufficiently obscure that his birth and death dates aren't known for certain.

Waldseemueller appears to have also known something about the contours of South America's west coast years before Vasco Núñez de Balboa crossed the Isthmus of Panama and Ferdinand Magellan sailed around the bottom of the continent. History books record them as the first Europeans to bring back knowledge of the Pacific Ocean.

The evidence of this knowledge is in Waldseemueller's world map of 1507, perhaps the most valuable of the 5 million maps owned by the Library of Congress. It was acquired for $10 million in 2003 and went on permanent display last year.

The map -- in near-perfect condition and with no other known copies -- is the oldest document that applies the label "America" to the land mass between Africa and Asia.

This was, of course, in honor of Amerigo Vespucci, a Florentine navigator who had sailed to the New World for the Portuguese. (His first name was Latinized to "Americus" and then feminized to "America.") The act of naming was apparently Waldseemueller's alone; there is no evidence that the term was in use at the time.

New research by John W. Hessler of the Library of Congress has made the mystery of Waldseemueller's knowledge deeper and richer. But it hasn't answered the biggest question: How did he know?

"There is some probability that Waldseemueller knew something that is no longer extant -- information that we don't have," Hessler said....