This story should be understood against the background of the internal exploration of Latin Christendom in the late Middle Ages. The search for the origins of the vocations of European explorers can only be rewarded by taking a very long-term view and acknowledging that the process grew, cumulatively but slowly and unevenly, from modest beginnings. It can be traced, in a sense, to Latin Christendom’s era of self-discovery in the late eleventh and twelfth centuries, when the riverbankers conquered the wild wood, in a vast project of the domestication of little-explored and underexploited environments, while observers and travellers turned inward to find and describe Europe’s inner barbarians: the remote peoples of forest, bog and mountains, the imperfectly assimilated marchland-dwellers, whose evangelisation was sketchy, at best, and whose habitats were often blanks on the map. At about the same time, knowledge of the world beyond these recesses and thresholds was increased by the colonists and crusaders who extended the frontiers of Latin Christendom. Scholars in western Europe were acquainted with the vastness of the world by the experience of the crusades — reinforced, in the thirteenth and early fourteenth centuries, by the reports of merchants and missionaries who travelled the Mongol road as far as China or sailed, with indigenous shipping, on the Indian Ocean.
The map had to be pieced together gradually from a number of sources. Two of these went back to Roman times: the map of Roman roads preserved, among surviving medieval sources, in the fourteenth-century Peutinger Tables in Vienna; and local surveying techniques, the continuity of which is suggested by fragmentary survivals of maps made by the Roman agrimensores and their successors. The estate maps of wealthy monasteries could cover vast areas that were sometimes widely separated from one another. Estate management and the collective business of widespread religious orders generated itineraries — essentially, lists of stopping-places. Pilgrimages and royal progresses also yielded itineraries, which survive in map form in fairly large numbers from the thirteenth century. As their traditional, linear patterns were modified by the surveyors’ tradition of rendering spatial relationships, so area maps evolved. The needs of warfare were an increasing stimulus to the development of techniques: the crusading propaganda of Marino Sanudo, for instance, was illustrated with maps of uncanny accuracy, made with the aid of a grid. In the fifteenth century, maps gradually became part of the regular equipment of field commanders. Maps like those made for Sanudo by Pietro Vesconte, covering areas not previously mapped by Christian hands, are documents of exploration, as are those derived from Nicholas of Cusa’s fifteenth-century maps of Europe between the Baltic and the Black Sea, including regions only lately and imperfectly incorporated into Latin Christendom.
A similar evolution turned written sailing directions into marine charts during the thirteenth century. St Louis, voyaging to Tunis in 1270, had one, and the earliest surviving examples are of not much later date. Though the concept of scale was not applied with any rigour until well into the sixteenth century, as instruments for recording routes by land and sea the products of late medieval cartography became highly serviceable.