The Martellus map of the world
The word Mediteranean means middle of the Earth and for many centuries that’s how it was depicted on maps. In Magellan’s time the most authoritative map of the world was that by Claudius Ptolemy, the great astronomer and geographer of second century Alexandria. No doubt Magellan knew it from his studies at the Portuguese Institute of Navigation sponsored by Prince Henry, known as the Navigator although he never went to sea.
As the Portuguese extended their empire they added to their knowledge. Map-making was a growth industry and maps of new worlds were guarded as State secrets. Magellan had access to a number of maps and globes, some more accurate than others. None of them featured the strait at the tip of South America that was later to bear his name.
The problem was not only the lack of information about distant lands but also the difficulty of rendering a spherical Earth on a flat sheet of paper. Men of science no longer doubted the world is round but the mathematics and techniques of cartography were in their infancy. Prominent Portuguese mathematician Pedro Nunes was the first to produce a formula representing a rhumb line, or loxodrome, by a straight line on a map. The importance of this is that the rhumb line is a constant compass direction as steered by a ship. Gerard Mercator extended the technique and his name now describes the familiar map of the world seen in atlases and elsewhere. The Mercator chart is still an idealised representation of the world. It suffers from severe distortion in high latitudes and the latitude or distance scale is not uniform.
A great difficulty facing medieval navigators was that maps of their day truncated or omitted the Pacific Ocean. They knew the circumference of the Earth was 360 degrees but no one knew how many miles or leagues there were in a degree of longitude. Columbus and Magellan both underestimated the circumference of the Earth by about one third. This almost led to failure of Magellan’s expedition due to death by starvation and scurvy. No one had previously imagined the vastness of the Pacific Ocean.
In 1962 an anonymous donor presented Yale University, USA, with a long lost map drawn by German cartographer Martellus in the late 15th century. It was in very poor condition but new techniques enabled researchers to peel away layers of dirt and enhance images with electronic scanners. Historians speculate Christopher Columbus may have known of this map and, if so, Magellan would have known of it too. It is thought to have been influenced by information brought back from China by Marco Polo. It is intriguing for the inclusion of considerably more detail of Asia than other maps of the time. It features an image of a castle supposed to represent Paradise. Columbus claimed to have discovered Paradise on his final voyage but historians believe that Columbus’s Paradise was the Orinoco River. The Martellus map shows a greater extent of South America than contemporaneous maps. If Magellan did know of it, this could explain his utter conviction that a strait lay at the tip of South America known as The Dragon’s Tail.