The theoretical roots of the work of Fra Mauro (active ca. 1430-ca. 1459/1464) can be traced to the thought of the Franciscan Paolino Veneto (ca. 1270-1344), who began his career in Venice, later worked at the papal court in Avignon, and in 1324 became the bishop of Pozzuoli. In his geographic treatise entitled De Mapa Mundi, Paolino defined the function of world maps as to combine “text” with “image” to create pictorial representations of the habitable world and its peoples.
Consistent with the classical Greco-Roman principle of studying the geography of the world’s peoples in order to understand history, Fra Paolino attributed to world maps a pedagogical duty to exemplify Christian eschatology. Fra Mauro followed this paradigm as he transposed into written and pictorial form all that he had learned from his textual, cartographic, and oral sources.
From a technical viewpoint it is still uncertain exactly how the map was put together. The wooden support is made of three horizontal boards kept together by three battens. Upon this flat surface Fra Mauro glued four large sheets of parchment. Then he must have traced out the circumference of the map and the four diameters indicating the directions of the winds by adopting a well-known geometric method requiring only a divider. Upon this simple geometric construction, which may have been lightly incised with a stylus, he then proceeded to mark out the geographic outlines of the landmasses based on partial maps he had at hand, most of which have been lost.
One of these partial maps must have been similar to the marine chart, now in the Vatican Library, which had been produced in his own workshop and can be exactly superimposed over the world map. The minimal differences in the two maps can be attributed to the deformation and shrinking of the parchment surface over time. Usually maps were reproduced in copy by using tracing paper, with both the existent map and the blank parchment mounted on frames. The existent map was laid against the blank parchment, and backlighting was used to increase transparency.
Given the size and shape of the world map’s four parchment sheets, which were almost certainly glued together before drawing began, we can presume that the partial maps were copied using a carbon paper technique, which consisted of sprinkling coal dust on the back side of the map to be reproduced, and using a stylus to leave a trace of coal on the underlying parchment. Once he had marked out the coastlines, the cartographer proceeded to draw by eye the rivers, mountains, roads, cities, and temples. Place names and cartouches would be added in a successive phase.
The density of information in the Mediterranean and northern European territories makes it clear that for these areas, the drawing and the adding of place names must have taken place simultaneously. Outside of these areas, on the other hand, many place names were marked in draft copy, and only later would the craftsmen write the name neatly in black, blue, or red ink.
Multi-spectrum analysis has revealed that only very few corrections were made, which are generally of little importance both in terms of content and from an aesthetic viewpoint. This fact would lead us to imagine that the world map was a reproduction of a pre-existent model.