The mariner’s occupation, according to Columbus, ‘inclines all who follow it to wish to know the secrets of the world’. Exploration and geographical speculation fed off each other and were both reflected in maps which strained at the limits of geographical knowledge and aimed to include discoveries as they happened and conjectures as they arose. For it was not only the scope of maps that changed in the late Middle Ages but also their very nature. Until the thirteenth century — to judge from surviving examples — European world maps had been devotional objects, intended to evoke God’s harmonious design in a schematic form, appropriate, for instance, for an altarpiece. By the fifteenth century, mapmakers were showing the same interest in geographical realism as Renaissance artists in naturalism. Mapmakers collated the reports of practical navigators, who set out, in some cases, to verify the cartographers’ speculations. From 1339 onwards, the sea chart was a common medium for recording new Atlantic discoveries. Increasingly, this became the maps’ explicit role. The Genoese maker of an unpublished map of 1403 recorded how he had checked the details of his work against the experience and information of seamen. A famous map made in London by the Genoese Andrea Bianco in 1448 is expressly devoted to a record of the latest Atlantic discoveries of Portuguese navigators.
Marine and strategic charts were by their nature practical instruments and therefore susceptible to change and responsive to new information. The world map was encumbered with more tenacious traditions, derived from the genre’s devotional origins. The convention of depicting the world as the orbis terrarum, a continuous landmass, surrounded by islands and ringed by a circumvallatory ocean, was maintained by some of the most up-to-date cartographers throughout the period: for instance by Henricus Martellus, who included the latest ‘descriptionem Portugalensium’ in a map probably made in Florence in 1489. It remained usual to show the earthly paradise at the extreme orient and Jerusalem at least roughly in the middle of the world. Nevertheless, mappae mundi and globes were increasingly used to illustrate particular theoretical conceptions of the outlines of the world and the relative locations of places: most commonly, in the fifteenth century, those of Ptolemy, whose Geography, the text of which was translated into Latin early in the century, invited illustration to supply the want of original maps and to render the sometimes difficult language intelligible. Other examples from the fifteenth century include German maps which display unknown antipodean continents; the lost map made by Pietro Paolo Toscanelli of Florence, before 1474, to illustrate his theory of a navigably narrow Atlantic; and the Nuremberg globe of 1492, traditionally attributed to Martin Behaim, which seems designed, at least in part, to suggest the accessibility of the island of Cipangu, reported by Marco Polo.
Even in world maps — which gave their compilers a welcome chance to speculate about the fabled splendours of the Orient and the Indian Ocean — the greatest concentration of novelties was to be found in the fifteenth century in depictions of the Atlantic. This shows what a stimulus to the imagination Atlantic exploration was and how consciousness of an exciting and exploitable Atlantic space developed. To the mythical islands commonly assigned imaginary positions in fourteenth-century maps — those of Brendan, St Ursula and Brasil — a Venetian chart of 1424 added large and alluring islands, including ‘Antillia’, the latter identified with the island of ‘Seven Cities’, to which, in a legend not unlike that of St Ursula, Portuguese refugees from the Moors were held to have repaired in the eighth century. These islands became standard in subsequent cartographical tradition and inspired voyages in search of them. As late as 1514, Portuguese official sailing directions gave courses to islands ‘not yet discovered’ and one of the most amusing forgeries of the sixteenth century is a spurious Spanish ‘chronicle’ of the conquest of St Brendan’s Isle. Attempts have been made to relate these mental wanderings to possible real finds, usually in connection with theories of pre-Columbian discoveries of America. But once one appreciates the genuine excitement aroused in the fifteenth century by the unlimited possibilities of the Atlantic, the fertility of speculation seems adequately explained.
Fresh discoveries were a direct stimulus: the Majorcan cartographers who first placed the Azores roughly in their correct position in maps of the 1430s also introduced new speculative islands into the tradition. Andrea Bianco was interested in the latest verifiable novelties, as his sea chart of 1448 shows, but in his world map of 1436 he scattered imaginary islands about the ocean and even in the 1448 chart he included some traditional isles, with an assurance that an ‘authentic island’ lay 1,5 00 miles out in the equatorial Atlantic. Bianco seems to have felt that ancient certainties about geography had to be discarded. The same point was made implicitly a few years later by his collaborator, the acknowledged master of the Venetian cartographic school, Fra Mauro, who confessed in a note on his world map of 1448—60 — the fullest then devised — that his delineation must be imperfect, since the extent of the world was unknown. The geographers of the fifteenth century were like prisoners-of-war who, unable to see their cell walls in the light of a tallow candle, could imagine themselves free.
The freedom of conjecture can be sensed in the speculations of academic geography as well as in the mapmakers’ fancies. The dividing line between travel literature and academic work in this field or, within travel literature, between mirabilia and genuine reportage, is, in the case of some works, hard to define. The Indian Ocean experiences of the Venetian merchant Nicolo Conti, between 1414 and 1437, were represented by Poggio Bracciolini who wrote them down, as a moral tale ‘of the fickleness of fortune’ but they were full of facts which passed rapidly into geographical textbooks and scholarly maps. The Travels of ‘Sir John Mandeville’ are notorious, among fourteenth-century works, as the fabrication of an armchair traveller, but it is also a persuasive treatise, arguing for cosmographical propositions: the sphericity of the earth, the navigability of all oceans, the accessibility of all lands, the existence of an ‘antipodean’ world. Marco Polo, dismissed as a fable-monger by some, was justly appreciated by others as a true reporter of real observations. Columbus’s indebtedness to these two last-named texts shows how such works could influence and inspire explorers.
Though historians’ search for connections between the ‘Renaissance’ and the ‘Age of Discovery’ has sometimes been conducted with an air of desperation, it is also true that more learned texts, including rediscoveries from classical Antiquity, could also contribute to the atmosphere of speculation in which explorers’ expeditions were launched. Notable cases from the fifteenth century are those of Ptolemy (fl. second century ad) and Strabo (d. 19 ad). Ptolemy’s Geography became the most widely used geographical book of reference in Latin Christendom in the fifteenth century; it helped to inspire influential geographical treatises by Aeneas Sylvius Piccolomini and Pierre d’Ailly; it was read by Columbus and ransacked for points in support of his project; and it included speculations about the nature of the Indian Ocean which Portuguese expeditions in the 1490s may, in part, have been designed to test. Strabo was particularly important for the stimulus he gave to debate about the possible existence of the Antipodes; his text arrived in Italy in 1423; some of his ideas circulated widely from the time of the Council of Florence in 1439 (a great occasion for the exchange of cosmographical news as well as of ecclesiological debate); and a translation into Latin was in print by 1469. Though his references to the Antipodes sound ironic, they seem to have helped to convince geographers of humanist inclinations or sympathies, before Columbus’s voyage to the New World, that the tradition of an unknown continent or continents in the ocean was valid.